Bit of an oldie but seeing as no one's answered you I might help future posters:
You can't really go wrong if you just start with a low-level warband and help yourself.
Exploration of character and warband builds is half the fun.
That said, I enjoy Frenetic's guide to the Possessed myself.
Even though I haven't seen a Ripper Mutation in over 200+ days as a Possessed warband in v18.104.22.168.4