i doubt that will fit into your stock mounts, but someone has done this before so it might, hong nor cars are good, dont know about there engines, it will use quite a bit more fuel, bigger engine=less revs so to get the same speed from a .21 on a 15t you would need a higher tooth pinion on a .36. probably louder but would be a deeper sound rather than a high pitched .21, 25% will be fine, 0s n0.8 should be ok, jp-3 will work fine but a jp-4 would be better.
But i wouldnt go for a .36 because you wont go faster just have more torque, and a buggy wouldnt need that. I would go for a .28, or .30 LRP at most, they should give enough power and there is more choice available.