Leaving the frames in? How wide?

Re the Petrel 28 mentioned previously, the cost of the plans is 850 euros (approx US$ 1,000) - these plans appear to be very detailed. And if you did build a boat like this, the odds are that the cost of the plans might only be 1 - 2% of the final cost.
Petrel 28| family cruising sailboat | small boat plans http://www.modernwoodenboat.com/mwb_project/sailboat-homebuilder-petrel-28/

Have you come across the Van de Stadt designs? The Vita 30 might be suitable for what you have in mind (?). The cost of plans for her is approx US$ 1,200
Van de Stadt Design - Vita 30 https://www.stadtdesign.com/designs/stock_plans_sail/vita_30

RM Yachts do not sell plans, but they build plywood multi-chine boats with twin keels - have a look at their 890 here. With twin keels her draft is a bit under 5'.
Notice the lack of framing in the photos when compared to your design.
RM 890+ EN - RM Yachts https://www.rm-yachts.com/en/rm-890-en/

Here is a shoal draft (3'2" draft with the board up) design by Paul Gartside - but she is traditional plank on frame construction.
Gartside Boats | 26ft Shoal Draft Cutter, Design #193 https://store.gartsideboats.com/collections/sailboats/products/26ft-shoal-draft-cutter-design-193
Paul notes that the building time is 5,000 hours - at 25 hours a week (which is probably rather optimistic) that is 200 weeks / 4 years. Bear in mind that any boat building project will take a long time......

The electronic plans for the Whisstock Sapphire 27 appear to be very detailed, and are available for US$155 - it would be worthwhile buying a set just to learn from re your design.
Whistock Boats and Boat Plans – Design 056 https://www.whisstock.com/page_02.php?page_id=2.4.2&design=056

Here is the Multichine 28 design by Roberto Barros -
B & G Yacht Design - Multichine 28 http://www.yachtdesign.com.br/ingles/projetos/mc28/desc28-2.php
Have a look at the list of plans that are supplied - you would have to do something similar (re quantity of drawings) for your design.

I had mentioned the Devlin plans earlier - Means of Grace would be a comfortable wee yacht to take you to the Caribbean, if your river can cope wth 5' draft.
And you can download a set of plans for her for US$ 255.
Means of Grace 28 https://devlinboat.com/means-of-grace-28/

Or Sam's multi-chine plywood Onyx 28 (draft 4'6") - a downloadable set of plans for her costs US$ 206.
https://devlinboat.com/onyx-28/

 

A real gift to the OP.

 

You posted a design of an outboard powerboat. That is a horrible shape for a sailboat. There are hundreds of books on boat design. The common sense of boat design by Herreshoff, Skene's elements of boat design and Elements of boat strength by Gerr will get you the basics. However, the understanding of the functioning of a design is something that takes years of study and experience. As many amateurs, you are hung up on designing and building your own boat. Your first boat will be a prototype. That is where you learn what mistakes you made designing and building. The idea that it will be the perfect boat is a fantasy. To start with, if you want a hull with a large angle of vanishing stability, a wide shallow hull is wrong.

 

Gonzo has mentioned some excellent reference books above - this one is also very good, in that it explains the basics very clearly and simply.
https://www.amazon.com/How-Design-Boat-John-Teale/dp/157409050X/ref=sr_1_1

Even though you can work up a 3-D model of a yacht using CAD, you still need to have a good appreciation for waterlines, stations and buttocks and how they relate to each other. It also mention a lot of the work needed that is not so glamourous.......

John, building a boat yourself is a serious investment of time and money - and for this you want the very best possible design to suit your intended SOR.
And to put it bluntly, this design will be much more achievable if you buy a set of plans that are close to what you have in mind, rather than trying to design the boat yourself from scratch.
Once you have a set of plans you can always modify them a bit, if you think you can improve on them in relation to your SOR - but be careful.

 

Ooof, $650 usd is a bit much for me to spend on a book haha.

I figure if I keep chugging away at the design, I can slowly narrow down problem areas and keep correcting until I have a solid plan that a naval architect would approve of.

Eventually I'll start making models of the design and testing it in my lake and whatnot. I'm not looking to come up with a perfect plan overnight, it will surely be a process to get it all sorted out and all of the issues solved before the first piece of wood is cut.

I've never seen a boat that is trying to do what I'm aiming for. But larger catboats do come close (just I don't think they are really designed safe enough for the sea).

Thanks for all those examples. But sadly none of them are really what I'm looking for. A standard 28 foot boat is a bit cramped for what I'm aiming for. ((It only works with the one I'm trying to design because of the more generous beam, making it a lot bigger boat than the length suggests)).

A wide shallow hull is what catboats and sandbaggers used...

But, yes, it needs additional design considerations to have a large enough angle of vanishing stability for safety (which is why I was thinking the drop down keel and some other measures). The wide beam definitely is a challenge to achieve these goals over a conventional sailboat, but I don't think it is an impossible task (though it will require some sacrifices to performance, no doubt).

 

Where did you find one for sale for $650? Amazon say that they have 16 second hand copies for sale from $4.50.

I don't think you have yet posted a list of requirements for this boat? That would be useful.

Are you ABSOLUTELY limited to a length of 28' overall?
If you are, then I doubt that you will find a 28' yacht that has as much very useful and ergonomic accommodation as the RM in the link above.

Maybe you could start off with something like a MiniTransat 6.50 with a scow bow (as per the link below), and 'stretch it by 2 metres to about 8.5 metres or 28'?
Presentation of the Maxi 650, the new Mini series of the idbmarine shipbuilding yard in Finistère https://www.idbmarine.com/en/maxi/650/maxi650.php

 

A lot of the criteria are subjective. Such as "a decent amount of room for a single hander".

But generally what I'm aiming for is

1. greater initial stability (more comfortable)
2. moderate sized craft (35 foot+ is pushing it for single handing)
3. maximum livable space (as close to a 32 foot - 35 footer as I can get)
4. a boat with a shallow draft (enough to get down the Kansas river and Missouri river into the Mississippi)
5. self righting (or at least rightable at sea)
6. "unsinkable" with positive buoyancy
7. average sail speed of at least 4 knots
8. heavier carrying capacity (which is why I'm not aiming for a catamaran)

Basically giving up speed for everything else in a boat. And I think it's achievable if I just take a catboat and try to solve its weaknesses at sea (mast placement and angle of vanishing stability).

So a wide beam + a drop down keel + mast buoyancy .... in theory it should give all the advantage of a catboat (comfort, speed) while letting it be safe at sea with a greatly enhanced angle of vanishing stability (and even into self righting territory, since mast buoyancy will get it back to its stable angles)

BUT, the trade off is that by adding those features, the performance will be hit. Which is fine since these boats already are strong performers.

Nope, just seems like a good length for a single hander. Not too big, not too small (as long as the beam is wide enough).

Those are interesting boats, it's similar to what I'm after. Uses the same concept of wide beam + swing keel to keep it self righting. Too bad there aren't plans that take it bigger (just scaling it up seems like a bad idea, since the forces and structure are very different at different scales).

That's why what I'm proposing doesn't really seem that pie in the sky to me. Between those racing boats and sandbaggers and catboats, wider boats seem like they perform very well (even when made full wood and heavy, like racing catboats and sandbaggers traditionally were).. and from what I read, they are also much more pleasant to sail and comfortable. Just as long as you can solve the turtling problem for going to sea (which mini transats do).

Throw on things like modern unstayed carbon fiber masts and you are already starting to simplify the design to save a lot of headache (no chainplates, no stays).

Must be a weird glitch?

 

It is all very well taking a catboat style of hull but when / if she goes over she will be very happy upside down, and you certainly won't be able to right her yourself.
Very very few ocean cruising yachts still have positive stability through 180 degrees - and if they do, then it is usually with caveats such as the boat is totally sealed (hence no water ingress) and no excess weight stowed on deck (dinghies, O/B motors, liferafts, extra cans of water, all add up).
Just look for a design that has a positive righting lever up to around 130 degrees, as per the graph (copied below) in this link -
How Gz Curves Reveal the Truth about A Sailboat's Stability https://www.sailboat-cruising.com/gz-curves.html



Re making your design unsinkable, then you need to have water tight bulkheads in the boat as well, and that starts to get complicated.
Ideally you want to have it such that any one compartment can become flooded, and you won't sink - and ideally you want to still have enough floatation / freeboard so that you can carry out any repairs (bung up the hole?) and pump her out.

If a 28' version of the 6.5 m Mini Transat scow would meet the space requirement, then you could try scaling it up and see how it looks - you are only makng it longer by 2 metres.

Re John Teale's book, that is very strange - your screen shot is even saying it was published in 1727!

Here is a screen shot re what comes up for me :

 

I think that after so much advice, all very good, what you should do now is draw up an SOR as complete as possible, draw a General Arrangement plan, even if it is freehand, and ask a professional to define the hull to best fits all of the above.

 

To the books Gonzo already mentioned you can add Principles of yacht design by Larsson and Eliasson.
You keep mentioning a catboats wide beam, so I will try to explain something: a lot of boats have a L:B ratio around 3.x:1, and there is a reason for this, it offers a good compromise between sailing angles and accommodation. Going lower is possible, and even routinely done in some cases (like the minis), but comes with its own set of problems, usually related to upwind sailing. The scaled up scow bow mini has been done, it's called the Revolution 29, Accueil - Afep Marine https://www.afep-marine.com/revolution29-bateau-aluminium-presentation.php and I am sure the designer would draw you a 28 plywood version if you pay him.

Now to your list:
1. Greater stability by beam is not necessarily more comfortable. Upwind you either sail at heavy heel angles, or live with the pounding.
2. Lenght fixation is is outdated stuff, singlehanding a boat relates to its systems. Buy modern sailhandling equipment, put in a bowthruster and powered windlass and forget about it. Weight is the more important factor anyway, since that's what imposes limits on human strength and determines equipment size.
3+6+8. Weight, interior volume and unsinkable go together. To float one metric tonne (2204lbs) you need one cubic meter (35,31 cubic feet) of air (adjust for other flotation aid like foam by subtracting its own weight), and the goal is to float the boat upright in a stable position, it has to be in a certain position. Buoyancy chambers eat interior volume, and the heavier the boat is, the more you need.
5. Wide boats like to stay inverted, you need a cabin design that tips the boat enough for the keel weight to take over and right the boat.
7. Average speed means nothing without average wind and sea conditions. Good light air performance means additional sails, and those have to be carried and handled.

Going for a super wide boat only makes sense if you are lenght limited (by outside factors). Lenght only costs at the dock, and if you fill it with things. If you keep the weight down, lenght is your friend, the boat will sail better and be more comfortable.

 

That is a very nice boat.