While you are going to have your work cut out for you with 3 boys, it can be done. I have 3 females, 2 of which are pit bulls and 1 is a Chihuahua mix. It isn't a ideal, but it can work, it just comes down to management. There is a ton of great information on this forum, and the members run from new pit bull owners to hard core dog show folk to trainers and veterinary professionals, and everything in between.
Don't be scared off because of what you hear in the media. While bad things do happen, they are much more rare than one would lead to believe.
Your experience with Boxers will help you too. Yes, the breeds do have their differences, they have quite a few similaritys as well.
Welcome to PBF!