The Poke Pelago works like the Day Care used to, in that Pokemon in the Poke Pelago gain exp as you walk around, is that right?

How far into the game is the Poke Pelago? I want to dump some new mons in there that didn't make the team so they can get lots of exp while I play the story.

How many Pokemon can be in the Poke Pelago gaining exp at a time?