[Andrés]

I agree it’s impractical, but it was also impractical to send a ship to the moon.
IMO that’s the most plausible way aliens could get here.
Yes anyone embarking on such a mission would be saying goodbye to his/her/other(what sex can aliens have) home planet forever. I see that even if their cryogenics were good enough to send them and take them back during a lifetime, so long after they departed the world they return to would be as alien for them as any other they can visit.
I’m sure that if we had the technology to build such a ship, we’d do it. And it wouldn’t be so difficult to find volunteers for a 1 way trip to another planet.
If aliens are anything like us in that regard, they’ll do that too.

About multiple dimensions, excuse me if this has nothing to do with what you were talking about:
The same way you cannot place a 2D figure on a 1D line, or a 3D body in a 2D plane, you cannot put a 4D hyperbody in 3d space.
There can be infinite 1D lines in a 2D plane, infinite 2D planes in a 3D space and infinite 3D spaces in a 4D hyperspace.
Mathematically there can be any number of dimensions.

Unfortunately as we're 3D beings our minds have been designed to think in 3D, it's impossible for us to imagine a 4th spatial dimension.
Now imagine that the 1D line is not straight or that the 2D plane is crumpled. For someone moving along the line, or someone moving in that plane, it is impossible to see his universe is crumpled, you need to step out of their universe to see that. And when you do that, you can see that the shortest way between two points in the 1D or 2D universe is a straight line that jumps out of the crumpled universe.
This is the original concept of hyperspace, assuming that our 3D space is crumpled within a 4D hyperspace, and that you can find a shortcut by moving in straight line outside the universe.
Can anyone remember who was the sci-fi author that invented this?