the wishbones of the StockCar are made from steel, as are the wishbones in DTM, and most other race cars.
You will not find many race series which are using carbon fibre wishbones outside F1.
And you don´t want carbon fibre wishbones for your project, it will make it just more expensive - IMO. There is no need for it.
I don´t know much about Formula SAE, but what I know is that many of there parts are sponsored, so they get them for less then market price.
A formula SAE does not have 300hp and does not go 250 km/h, so I don´t think it is a good cpomparsion, to what you want to do.
As for the wheel fixation 4/5 stud is easier and simpler to make, and you will get more and cheaper rims/wheels for 4/5 stud, then for centre lock (one nut).
I would go with 4/5 stud for your poject, but it´s up to you.
If you don´t plan to have pitstops, there is not much need for centre lock.-IMHO