The shop is supposed to be in the game not discord.
True, obviously that part is negotiable. I just gave a rough idea of how the shop should be run, if it ever comes into existence. Deciding the prices is all on the devs
Your Unique Pokémon count doesn't increase if you evolve something caught before the current season, I don't see why the same can't be done with exp.
I really don't know of any reasonable way(s) to stop this, however i think that the one login at a time rule has stopped most people from abusing seasonals.