Theory/Question on Pain

So I rewatched the pain arc this past week and I thought of some questions about pain. First, where does all of his summons come from? Is there one place where they all reside, or did he travel and make a contract with multiple different kinds of animals? Also, I was always curious about the chakra recievers and how each pain had a different arrangement. I think thats because depending on how they were set up they channeled different chakra frequencies which lead them all to have different abilities