OK, it is possible that this universe is all that ever was, is or ever will be?
Yes. It is possible, even if you have a restricted definition of 'this universe'.
Again, language is an issue. Some, for example, talk about a multiverse, which would be a multitude of 'universes'. If you define the universe to be 'everything physical', this is rather nonsense. On the other hand, in such models there is limited interaction between the different 'universes', so this means it can make sense to talk about a 'universe' as being a causally independent (or nearly so) subsystem.
Do you think there can ever be such a thing as nothing?
No. To say there is nothing means literally that nothing exists there; even time and space. The word 'ever' already suggests the existence of time.
Do you believe in the eternal cyclic universe model?
I withhold judgement pending better data. I'm more inclined to either a multiverse with 'budding' universes or a universe that is finite in time.