I'm not sure I caught it quite right. You said you were planning on building an Aluminum frame and then making a mold or having a mold made for composites(CF)?
Two seater and as long as you keep the weight of everything low enough you can go total CF chassis/body and it will be as light as you can possibly go(at this point).
If. . .IF you are really interested. . .and it sounds like this project will take time to start with you could wait for CNRF(Carbon-NanoTube-reinforced-Fiber) which is cast to be at least 10 times stronger than CF and lighter still. That would allow even less material to be used, and it would still weigh less. Albeit. . .it would be pretty enormously expensive.
OH I forgot, with the CF though since you have a CAD package there are alot of Chinese manufacturers that will produce a CF monocoque just based on CAD images.
The advantage of the CF monocoque is you can get down below 1kip.
Aptera Motors has a Cd of .15.
Something to consider before you spend a chunk of change on aluminum