I'm also in a male dominated workplace, 4 women and about 50 men on my team! I was really lucky though that my co-worker was also pregnant and returned to work about 3weeks before me and was also BF'n. She had all the talks and answered all the many questions that the brave but clueless guys wanted to know.
As far as how to approach it with your boss goes though....I would just tell him the bare minumum of facts of what you need; ie. how often you will need breaks, how long they will last etc. Let him know he can ask any question that he needs, but unless he asks, I wouldn't toss out too many details. As a general rule of thumb most guys in my experience don't want to know the "details" of women things.

Also be prepared to let him know how BF'n benefits you as a working mom.....babies that get sick less often means momma has less sickdays!!