They were mutant possums of a semi-stable gene line, though they seem to be able to inter-breed with other marsupials, and offspring have somewhat random marsupial characteristics. They tend to have similar mutations to T'nimarv. This population was fairly small, and so there's no general name for their kind apparently.
A swamp that subsequently dried up, causing the possum family to have to split up and leave.
The swamp dried up early in his life, so although he learned a bit about wilderness survival there, more of his life has been spent on the road wandering from place to place.
The vast majority of what he knows he simply learned by experience.
Eat now, tomorrow the food may be gone.
Mostly how to scrounge, forage and beg food off of others.
He deals with the local archivists a lot. Not because he shares their cultish ideas, but just exchanging goods for food.
He has had several run-ins with Zoopremacist cats, who seem to have a special dislike for him and his scrounging ways, and there are a couple such in Highvale who run him off regularly.
Yes, several locations to forage.