Probably 34th level, since that's as high as you can go without stepping on the toes of the gods. But I might even go as high as 35th, making him on-par with the lowest gods in terms of power, but lacking the deity-specific abilities.
As far as role? I'd definitely focus his powers on disease effects (including necrotic and/or poison) damage, plus charming effects from his staff. So my first instinct is to say controller, but I think an argument could be made for making him a soldier, if one toned up the disease-based damage and toned down the disease-based conditions. In either case, I'd create a brand new, high-level disease to go with him.
This is, of course, all off the top of my head. If I actually sat down to stat it all out, something else might strike me as the better way to go.