All very true but one I can see one small problem with your idea.

"Also we don't know where our universe is expanding to".   I thought scientists say that all the galaxies are expanding away from each other.  So unless time and space curve back on themselves somehow they will never again get close enough to form another super-massive black hole.

In my theory expansion will slow and stop when the galaxies are in their appropriate positions within the new galaxy and it becomes "mature".  At some point in time after that it will then start another Big Bang as it begins to split.  The next big bang being the point when it ruptures its boundary into the next "layer" of the multiverse.