>>291718143 at best on my hand.
if PC storage is real and the mons basically don't even exist if they are data in the balls then you could truly just collect as many as you want and shit doesn't matter.
but for now three if it actually does matter.
grass types are very simple I imagine. so I'd probaby prefer them because they only eat sunlight and drink water. unless they get really big.
so maybe I'd own Lotad and Bellsprout.
third mon would a normal type. I'll go with either Kecleon or Lickitung. Kecleon is smaller so it eats less. Lickitung is probably gluttonous so probably not that. Porygon doesn't breath or eat, I think, so that's easy to keep.
for all faggots saying ghost types, well, I imagine you'll have other problems with these since they are living nightmares so enjoy your curses and deaths.