I'm not an electrician so I can't give you a number of what you should have for electric service but I will say go bigger than what you need for one 1200 barn.

If you put up one 1200 hd barn eventually you're probably going to decide that if you have to get stinky and do chores every day you might as well be taking care of more hogs.

IMHO put in enough electrical service for at least 2400 hd, maybe even 4800 hd depending on difference in cost.