Dave is obviously the man to talk to about the motor as you know and I can assist on the lightweight stuff.
First go with the notchback (non-hatch) for better rigidity and less weight (glass in hatch is heavy). Plus less equip. is required to install the battery in the trunk vs. hatch.
There are plenty of things you can do to lighten the car, I have already done some of them and will be doing more soon.
As far as a very skilled fab guy goes you could have John Moretti (partial owner of Coastal Dyno) do the work. He has a complete shop, lots of skill, and tons of experience.
I would think anything over 350 h.p. on a very light car would be a bitch to control unless you have specific data from someone else. I think the power curve Dave showed would be very ample in a light car.
Just my .02