Pasteurization will help the milk in many ways but I dont think it will have an effect on your soap one way or another.
My milk goats are a joy to own. But up-keep can be expensive, and remember they are a herd animal, so you need at least two.
The people your buying your milk from may offer you a different price if you tell them its for soap. As in a discount on "older" milk, since it's being soaped with it dosent have to be as fresh as drinking milk.... another thought is a trade, discounted milk for some soap? One other thing to look into (cause i know your in the great state of Tennessee!) is Goat Shares. you "buy into" a goat on a local dairy farm. In exchange you get "free milk" your a co-owner of a goat, most places will let you hang out on the farm and help( so your kids can see what its really about) But the farm owners shoulder the responsibility of true owner-ship.