Theory is essentially correct: You can get infinite with a single Possession, Council Room, Throne Room, and enough Masquerades. Pass them around as you play, and TR the Possession, doubling the amount of turns spent on the next player.
But if you're playing against one other accomplice you can get over 3000 cards in hand without passing the Possessions.
It involves several tricks: KC on a lot of things, Possession, Outpost, Council Rooms are the big ones, since you get 62 turns to get 30 cards each time. The first turn is possessed, and includes an outpost play, then the outpost turn occurs, then the 59 other possessions, then the normal turn.
To get another fraction one can use Torturers, then masquerade the curses back, then ambassador/moat them back into the pile. This takes 5 cards to increase the hand by 2, and I think with the remaining KC/TR you can net about 20 a turn this way.