Agree with Chris don't see how a very stable buggy designed for speed can also freestyle well, they just don't go together. Because of this all commercial buggies are a compromise to a point with bias either towards stability and speed - Libre Vmax, full race, Chameleon or towards tricking - Flexi, Peter Lynn, Parastorm Typhoon.
Will be very interested to see your design....
Answers to Qs:
1. What sort of price range are you willing to pay??
Unless you are offering something very different to what is already available you will have to undercut the establised brands which may be difficult for a small outfit
2, what sort of warrenty do you want ???
?? We would all like unlimited lifetime warranty but thats not really feasible is it? Guess 1 year is in line with everyone else?
3. Does it need to be foldable??
NO! Just able to be taken apart although if you can develop a system that works better than the PL folder may be interesting
4. how big or small do you want it. ???
Again as Chris this would depend on the buggies focus?
Also must have made significant progress and a lot of understanding since your last post last month :