No comment on the rest.
The first religion is usually thought out to be a form of shamanism, animism.
is thought to be the birth place of the first civilizations, if I remember right, so a structure like paganism wasn't seen until agriculture and civilization, leaving a lot of space. Shamanism/animism filled in the gap.
I could be wrong, this is just what I have read from a few books and heard from a few discussions.