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.