Sounds like a great project!
My advice is that you go as high with voltage as possible within your budget. The higher the voltage, the less efficiency is lost to heat in your cables and whatnot. You can go quite high before a Warp9 turns into molten lava - something like 192V is still within reason. Plus, when you want to have fun going fast, high voltage will put a giant smile on your face. Controllers do get quite pricey above 144V but many people say it is worth the investment. Keep searching the EV trading post for parts.
[EV Tradin' post] - Electric Vehicle Classifieds
You can register to get alerts emailed to you when something you are looking for goes up for sale.
Best of luck!