[Cor]

First does the province have a population around 5000? Because if its too much under that i would not waste my time.

Undead are immune kinda, they get the disease but the disease has no effect.
from what i have read Regeneration will keep a diseased person alive.
Yes, they can hunt while crippled or blinded, but mute, and feeble mind would hurt because they drop the blood magic.

As for defence, try bane bow archers, or try constructs.
Buliding a fortress could be really nasty. because they would have to siege...