What exactly made you decide upon the rear diffuser, verses, say, a front splitter or bumper canards? Are you building this from the ground up based on preliminary aerodynamic knowledge? Or, are you merely going to make a modified, more aggressive version of our stock diffuser i.e. larger strakes, etc. (I couldn't quite determine what you're going for from your previous posts, so I apologize if it seemed obvious)?
You definitely seem serious about the functionality over aesthetics. Are you basically going to fab some cardboard (or whatever material) prototypes up essentially out of nothing? Or, if it's possible, will you be working with CAD software to develop digital models and possibly even perform some flow simulations with those prototypes before making tangible models?
Also, how, exactly, do you plan on going about testing the functionality of your designs verses each other and verses the OEM unit? Wind tunnel? Time slips? The tried and not-so-true butt-dyno?
It would be one thing if you were designing your own diffuser mostly for aesthetics, but, since you're aiming for function over form, I'm very curious to see how you go about the entire design process and how the project evolves from its current phase to the final design. I've always wanted to undertake an R&D project like this for my car, but have always felt like I don't have enough money or available resources or knowledge to truly craft something uniquely functional. Hopefully, with more time and experience in the engineering field, that'll change in the future.
Good luck in your endeavor and keep us posted!