Hi there.
There are lots of expert ABers about, sso they'll probbly give you some great advice. When we got Jack, our Border Collie, we were told by the vet that the best time would be around 8-14 months for castration, so now seems a good time.
Behaviour isn't always affected, and if so it can as much as a couple of months after the op to see a difference. He might (or might not!) become less aggressive towards other dogs (esp. other males), stop marking his territory (esp. in the house!), stop humping (people/furniture/other dogs etc.), stop him roaming to find a bitch in season that he's smelt. They are the main ones, I am sure others can provide a more comprehensive list.
The op also calmed my dog's nervous aggression, and calmed his temperament a little, although he's a Collie, so it wasn't much!
It's a simple procedure; I was worried sick about leaving Jack at the vet all day, and about the op itself, but he just came out a bit woozy and minus his danglers! He doesn't miss them. I asked him.
Lisa x