If Profane Procession or Tomb of the Dusk Rose somehow has exiled cards other than with Profane Procession's ability, those exiled cards aren't linked to Tomb of the Dusk Rose's second ability. They can't be put onto the battlefield with that ability.

If you have enough mana, you can activate Profane Procession's ability multiple times before any activation resolves. It will be transformed if one activation exiles the third card. Further activations waiting to resolve won't cause Tomb of the Dusk Rose to transform back into Profane Procession, but they will exile creatures that Tomb of the Dusk Rose can bring back.

In a multiplayer game, if a player leaves the game, all cards that player owns leave as well. If you leave the game, any permanents you control from Tomb of the Dusk Rose's ability are exiled.

Profane Procession's ability can exile token creatures. They won't count towards the number of cards exiled with it.