The completely flat bottom aft is a combination of what I have read and what GPT calculated for an “optimal” lightweight planing hull. My understanding is that the larger surface area in contact with the water will get the most lift but you are probably correct that once on plane this becomes less desirable.
Flat bottom craft plane quite well, and naturally reduce their wetted area as speed increases. Adding deadrise increases wetted area, and also reduces the efficiency of planing for the same reason that adding dihedral in an airplane reduces wing effectiveness: the lift vector is no longer pointed in the optimum direction. In an aircraft, there can be good reasons for adding dihedral (such as augmenting stability), but those reasons are not for improving L/D. Thus HP sailplanes have negligible dihedral. In the same way, deep V boats are more comfortable, and track well, but are not as efficient as flat bottom craft, in terms of the power per pound to sustain a particular planing speed. All this is discussed in Savitsky's classic paper on planing resistance.
It is available here.
Dihedral taken to extremes ends up looking like a v-shaped catamaran hull, which has a snowball's chance of planing because the area is low and the direction of dynamic force is all wrong.
If you look at the Bolger design that Alan Craig linked, you will see that it is similar in key ways to your own design, in particular having a flat bottom that extends quite far forward of the transom. You could do worse than to follow in the footsteps of Bolger.
However, if you add some deadrise aft, the boat could be slightly lighter, because the keel will add some stiffness that otherwise requires stringers. (Deflection increases with the cube of span.) If anything, it is likely to be a little easier to build, because there is less twist in the bottom panels (less angular difference from forward to aft sections).
In a small boat like yours, you have a lot of control over CG location just by shifting the driver's weight. Taken to extremes, this sort of control shows up in windsurfers, which have near zero rocker and zero deadrise, and plane extremely well. At speed, only the aft foot or so remains in the water. I find it interesting, but not too surprising, that traditional windsurfers have been shown to be faster than foil boards. My microfoiler is an experiment, and at some point I will probably remove the foils and make it plane. I am not expecting a huge difference in top speed. For electric craft, I think there are intermediate speeds at which foiling is more efficient than planing that could be exploited.
You might want to read up on humpless planing hulls, something Frank Bethwaite wrote about. I played around with a humpless design on my Windrocket, which under ideal conditions would do just under three times wind speed (or so my computer said -- I didn't have good windspeed measuring equipment on board). I had it going 32 knots in wind averaging 10 knots on shore. (I don't know how much higher it may have been on the water... but there certainly were not whitecaps). On the Windrocket, part of the means to lowering the hump was extremely low weight, and another was narrow beam (which would ordinarily reduce planing efficiency -- everything is a tradeoff). DLR was about 38.
