All correct. I believe it was in version 9 that we made a lot of enhancements so that these (what we call) Robo scenario's work and the data doesn't have to be sent over the wire all the time. So have your B&R server in Office B, have one server in office A that is used as a repository server (that will run the components such as the proxy and mount server etc...) and you are good to go.
And then indeed you have options... I proposed a backup copy job from A to B to have it offsite. But you might also want to consider (as you kind of say yourself) to replicate from the backups on the repository of office A to office B (means no more touching the production environment resources). So take the replica from the primary backup, not from the backup copy job (although that is possible also)
And for your last question... Yes, giving you even more options. Replicate the servers to that old server in office A giving you a quick solution in case a single server dies (or a few). Then have a backup locally also, and then do a backup copy job to offsite.
Lot's of possibilities