This kind of thread appears from time to time on the forum, the search function will yields plenty of identical discussions, but anyway.
The problem with ground effect cars is that they are very sensitive to ride height and attitude changes. If you want a predictable car (and not one that beyond 3% of a neutral position will lose half of its performance), then I would suggest to reduce ground effect features even if they are an easy way to achieve your goals.
I have developped a Pikes Peak car (check my blog
>> HERE <<) and you can clearly see there how pitch affects its performance for example (look at the splitter values precisely on "v2"). I am going to start soon another project on the green Fabia that can be seen on the blog but this time with emphasis on keeping or increasing its performance with yaw while avoiding too dramatical change in performance with attitude changes.
As the other said, I believe you have not got enough knowledge to "know what you are doing". As tempting it can be to throw CAD into CFD, learn the basics first, start with a simple model, have it correlate with results you can find and then put your own model in, starting simple (no cascade wings, etc).
I haven't got lots of aero experience, but these are points I've learned along the way.
