Yes, planets are fine domains. I imagine they'll be close together for the most part, just so one specific part of the universe is analagous to a sort of "heaven" (minus the cloud imagery). Each god would have their own planet, and other gods can meet them there (or send messages for a god to come to them). I do believe it's customary for the gods to show respect when on the other's territory. I do also agree that that they have preferred, often humanlike forms that they take on. I wouldn't call those forms "mortal," though, since that would suggest that they are at all vulnerable.

Your idea of where the gods come from is a fascinating one, I'll gladly integrate it.

Your idea of a new god being one that wants to create life is fine by me. You can make a character like that. Of the two characters I have in mind, one is largely in favor of creation, while the other is largely against it.