Besides the aviaries there's also a classroom, bird observatory room (where they do bird banding demos), the gift shop and this hallway. That's basically it inside the building I believe. I'm going again tomorrow so I'll see if I missed anything
There are indeed bathrooms in the lobby, they're kinda hidden behind walls so while easily accessible they're not easily noticed. The womens room is next to the bird observatory room, mens next to the classroom. Or once you enter the building and are facing the arch the women's bathroom would be on your right, men's on your left.