Bruce- I hope you are going to put a starter motor on this. Maybe you can model it after ours, since it is lightweight and hasn't failed us yet after 1000's of starts.
Sparweb- We do use the strength of the carbon fiber, since the shell is integrated right into the frame. Our window from last year was WAAAY too big, which hurt us in stiffness and weight. A much, much smaller window is planned for the next design. The structural part of the car is mainly to support the driver and the drive train, since the passenger usually weighs more than the car. Also, since there is no suspension, things have to be extra strong to take the shock loads.
Our car that we ran my first year was made of fiberglass. It was a little bit heavier than carbon fiber, but very weak, so it was reenforced with rope and steel strips. The shell alone was probably 40-60 lbs, and this only covered the top half of the car. The frame was made of 0.032" aluminum and pink foam, which proved to be very, very good. From an engineering standpoint, it was pretty much perfect. The carbon fiber rails of last year's car were good too, but they had too much carbon fabric and glue... probably 5x too much. A 2" tall by 1" wide 2-layer thick frame rail set up could support about 500-1000 lbs easily at 48" long.
There was a team last year that used the aircraft skin stuff, which was great for the lightness, but bad for a smooth aerodynamic shape. It doesn't matter which way you put your "hoops" (longitudinally or laterally), there will be all kinds of aero problems. That being said, a car that gets 2000 mpg (with an okay engine) could be built with the aircraft material or fiberglass. The carbon fiber shell could be made for ~$300 in glue and carbon fabric + a male or female of your choice. Building the mold as you described it is probably close to the best way without a cnc. Female will offer a better surface finish, but a male gives you a better idea for how the car is actually shaped. For us, this will be our last car that we get to build, so it is going to be perfect. Based on our experience building the first car, getting the shape smooth and how you like it is an immense amount of work and is very hard to achieve. I'm guessing about 25% of the teams last year had a CNC machine do the work...
Also, carbon fiber is very easy to work with, especially for people who have never done anything like this before. If anything isn't strong enough, just add another layer or two and it will be fine.