Are there any limits in using computer players for custom multiplayer scenarios?

Say I'd want to make a 2PvE (2 Players vs. Environment) scenario where two human players have to cooperate in beating an AI/computer player, with triggers being present in the scenario. Are there any restrictions that would prevent me from making such a scenario? Would a third player be able to take over the computer's slot? Would triggers even work?

Also, while I'm on the subject, can you set the player colours in the scenario editor and have them stay once the game is played in multiplayer?

Thank you!