True, although in BDSM relationships, the sub is overall in control because they set the boundaries of what's going to happen. Although again, that has a similarity to WG encounters.
Totally true, which is why communication is such a vital component.
The girl needs you to stop and step away when she uses a safe word like "red!" for example. Not when she says "oh my god, please no!"
It's the difference between roleplaying and having fun or reaching a limit and causing the roleplay to be suspended.
As a Dom, it is important to exercise restraint. Even if you really do know exactly where your subs limits are it's fun to start at a lower level and build up, explaining everything you're going to do before you do it.