I like multiple dimensions. Well, sort of. But the idea is, if you go back in time, you create a new universe in which you went back in time. You can never get back to the original universe and that universe goes on with out you.
Not really, let's keep the idea of just one Universe. You go back in time, it's the same place, and then, you suddenly go back into the "present", of course, with the changes triggered by the actions you have done. It would be the same dimension, though which has new horizons for the future.
We don't need to talk about a multiverse and/or multiple dimensions for this. Of course, adding them would mean a brand new theory, which doesn't attract me too much.
As far as traveling back in time in general, the only way to do this at the moment (theoretically), would be to travel faster than the speed of light which may be possible, but only if you want to go into a blackhole. And if you're going into a blackhole, well, I don't think it will really matter. So in short, I think traveling back in time is currently impossible and that it most likely always will be.
No. Going faster than the speed of light yes, can bend the time, but it still flows. That's what different tests suggested until now at least. Everything more, are just theories.
Though, about the black hole, I must say I totally disagree with you. A black hole is just a star that sadly died, and which has the interesting attribute to absorb even its own light. It's
very heavy, so, it has a mass, a body. Rest, it's just SciFi related to them.