I just realized you need an unemployed serf to produce $$.

Since the serf isnt doing anything can they explore around for treasure? or any other good use to put them too while they produce $$?

Do they have AP?

. Do i need to be concerned about serfs getting attacked, either by orcs or other players?

Serfs only produce gold when they are not doing "anything".
Thats when they are wearing that white get up.

Anyways, they cannot be attacked by anyone, however destroying the town counts as killing the serfs. And they dont have AP. So you can take them anywhere as long as they are in the city boundary.
But sadly, they cant pick up treasure chests.