You wouldn't want to put a rack on a suspension fork or a road bike. On those you would mount a bag to the handlebars. Just about any other kind of bike, it's fine. It's absolutely no problem to put a rack on the back or the front of an average commuter bike.

Brakes would not be a deciding factor for me. I like disks better but I've had brakes of all kinds that stopped fine and none of them seemed complicated.