First off, I much prefer
Bo.
Beau is too much of a word...it means "beautiful" in French. I have an issue with any name that is an everyday word in another language, especially that word. That being said, I
kind of like
Belle as a middle name haha.
I guess
Bo is kind of cute. A bit silly and cutesy, but on the right person it would work. I'd prefer it as a nn, although the only full name I can think of right now off the top of my head is Bogart, which I don't like.