Questions about the universe

I know there's no way to give a concrete answer for this, but what's your best guess?
Is it finite? If it is, what's on the other side? Perhaps a parallel universe? Can we somehow access that parallel universe? If we can't, what's blocking us? What marks the end of the universe?
Is it infinite? If so, how? Does it simply keep expanding? What if someone teleported to the current end of it, then would they see a temporary ending?
Thinking about this stuff alone gives me headaches. :P

As you have stated no one knows.

The most convincing evidence we have for answering these questions is found in mathematics. Very complex and well worked equations have yielded numerical outputs for things we have yet to observe. This is what string theory, and M-theory, etc... are. They are extrapolations on equations from quantum, and those involving dimensional space.

It's somewhat well accepted within the scientific community at this point that the probability of the existence of extra dimensions is good. Obviously we have no direct proof yet so science is skeptical, but our math allows for it, so we will continue the search.

A multi-verse is a topic the scientific community, as far as I'm aware, is still on the fence about. There are proponents and disbelievers.

One of the main arguments now for the multi-verse is the inequalities in the microwave background radiation. There are spots where it's "warmer" and spots where it's "cooler". Some theories posit that the "warm" spots are caused by gravitational pull from other universes.

If you look up "dark flow" it will give you more on this.

As far as infinite or finite, I believe that whatever our universe/multi-verse is, is altogether infinite, or infinitesimally large.

Part of my argument for this is, the seemingly impossible number of larger and smaller scales we've observed thus far.