I don't mean to be contrarian but you could side with the bad guys(and be the antagonist) in older BG games.
Kind of. You couldn't side with Sarevok in BG1 and you could temporarily side with Bodhi over the shadow thieves in BG2 but this game seems like it's going to give the option to fully side with the villains.
Originally Posted by Argonaut
5e rules do not prevent prebuffing either
I didn't say it did but concentration prevents just stacking a ton of them before every hard encounter. You can prebuff but each caster can only have 1 buff active at a time.