RE: size of esc, bigger is better?
The only (small) disadvantage of buying a bigger ESC than you need is a small weight-penalty and usually it cost more. No problem to run a 36A ESC at only 15A WOT.
In fact it is better to have electronics specced for more than you load them at, because loading at max-rating might cause things to overheat and fail. If the few extra grams is not an issue just buy the 36A and be happy.