Have some Crazy Ideas about converting a Tug

Hi All, I am new to the site and have a medium level of knowledge of things nautical. About 5 years ago I purchased a 28' carver that was an insurance total loss. I was able to repower it and fix it on my own and enjoyed many a gulf cruise in it. At the time I was single so it had plenty of room, but now 3 children and a lovely wife later I have the water bug again. I want a vessel that can:
Support 5 people for at least 14 days under way
Cruise 400NM unrefueled
Is costal sea worthy (25-50 NM offshore)

I don't have a few million to plop down at once to buy a shiny new toy, nor would I wan't to. I was thinking that I wanted a non displacement hull of steel for because:
1. I am not in a hurry
2. I wan't something that can take a beating in rough weather
3. If piracy is an issiue steel vs fiberglass /RIB factor

I thouyght that a tug like this would be ideal
http://www.boatquest.com/photos/0904051204241.jpg

I know that refitting will cost quite a bit but I like the work and that is the only way I could do it is a little at a time.

The things I would like to do would be:
Have a redundant electrical system , Can power off of prime movers/genset/trickle solar charge with battery banks

Have freshwater making capibility (Powered RO)

Autohelm ( I would most likely install rayethon raylink intergrated system)

I know I am a little off my rocker and was just wanting to get everyone elses input

 

Some of my specific questions

1. Building up the area behind the pilothouse, I am assuming that since this a tug the weight of building materials should not be a big deal as long as I keep it within sanity. I would like to turn the stern area into a cabin.

2. Mast with sail to increase range, Is their a mast/sail big enough in the world to help push a non displacement hull?

3. I like the old 2 stroke GM's but could I get more range and speed with some of the new Cummins BTA this boat currently has 351's