Wow where do I start? Maximizing the CL/CD ratio of a race car is kind of the goal of all aerodynamic work related to the car. There are so many considerations in balancing your drag vs your downforce from your front wing geometry, to the diffuser, to the shape of the body, rear wing etc etc. There is a lot of testing involved to achieve maximum performance from the car so if you’re looking for a definite answer to this, its a huge scope to cover.
From what I can input now off the top of my head is probably with regards to ride height. Lowering the chassis as close to the ground as possible would generate significant downforce for little change in drag, namely making use of ground effect. Ensuring that the flow at the floor doesn’t “leak” out the side as much as possible is also a way to maximize this effect.
There are plenty of more talented and experienced people around to help you with this and I hope to embark on a similar project like yours soon! Hopefully my earlier statement wasn’t incorrect
P.S F1 design books and looking at why certain designs are done in a certain way will certainly give you great ideas. Look there for inspiration and ways to optimize.