The marble will need to be very clean, to avoid “fish eyes”.
I never recommend any coating on marble as once the coating begins to deteriorate, is starts to peel. This can happen as soon as a few weeks and once it happens, you have a very unsightly piece of marble. Also, if you use a coating like a polyurethane, when it comes time to re-coat, you will need to strip the old coating off and this will require the use of very aggressive chemicals.
So in my opinion, I would not use polyurethane on your marble top.
The shine most likely will not last and and when it begins to break down, it will look very bad.
Use a sealer made to seal marble. it will penetrate the surface and protect it. When a drop of water soaks into the marble and doesn't bead up it's time to seal. Will need to be doe several times through the marbles lifetime.
I wouldn't recommend it.
Wipe on poly works well on wood surfaces. I use that as a top coat all the time. However, it shouldn't be used on marble. Clean the marble and use a product recommended by a counter top company - if needed.
No, I tried it on a side table and it peels off and leaves the marble dull.