Thanks for the feedback!
The arrow keys already work for the racing part, but I liked your suggestion. I've set it up for the next paid build so the arrow keys will also work when controlling Kaitlin, and Right Shift will work as an alternative key for boost as well. I can't promise a release date for the next free build just yet, though.
As for fully customizable controls, it's not something I'm currently working on, but it's definitely something I'd like to add in the future.
Regarding the performance in the main room, I'll see if there's anything more I can optimize there for a future update as well.