superstars or hypa hubs (trampaboards)
It sounds like you should be looking at an rc car not a skate board, and there is a good amount of open source stuff for object tracking, but I don’t think there is any ready made software for rc cars to do that, and gps would be too inaccurate for the road. Perhaps you could look in to having someone write you something, if you put a target on your bike it might be doable, a lot of work, but at least feasible, but I am by no means knowledgeable about object tracking ect. so I would double check everything I said. And much better to post on a forum for software/firmware/cs questions.
what you could do is used a brushed dc motor and have wired voltage control to the motor and just run the motor in reverse to break, it would be inefficient and kinda ghetto, but hey, if you want to make it supper cheap, it would work, though im not sure how powerful your breaks would be. Interestingly enough, the original esk8 boards used dc motors.
do you have the correct wheel pulley for your wheel type. The way the pulley should center its self, because it should fit tight enough to center its self.