Should my polyurethane sheen and paint sheen match?

Same sheen is a safe route, but it's all just opinions and a question of style. Personally, I'd say use a semi-gloss paint on the legs -- it's more washable than satin paint and the difference in reflection isn't much if any because the planes that'll reflect light at any point are small compared to the table top.

Just do a good paint/poly job and don't use flat paint unless you want that "shabby chic" or a dirty/rustic look.

Sheen=finish. It depends on your personal preference. Most tables have a high gloss finish on the top and a sort of flat or semi-gloss finish on the legs. Good luck with your project! I have never seen a table with a stained top and painted legs. It should be interesting!

No! Don't paint over a wall using polyurethane! It will make it impossible to paint over in the future!!! Instead of using poly, paint over the wall using the same color, but with a gloss base. Also, poly drips like crazy, is more expensive, and is toxic while wet. Finally, it will get really sticky before you finish a job that big!!! Just use house paint with a roller and brush.

I believe that I would use either a satin or high gloss finish for both. Since the tabletop will be seeing a lot of use, you will want to use the easiest cleaning finish. Since the legs will get beaten up by shoes (especially if you have kids) I would recommend the same. If you do decide to use two different finishes, use the high gloss or satin on the legs. That's where you will need the easiest to clean finish.

PS: To clean the legs when the get scuffed, use Mr. Clean Magic Eraser or the cheaper brands. They work great!

Use which you think best, but you can always clear laquer spray after painting to make it easier for cleaning & also giving the table a harder coating.

anything other than flat will clean up easier, just do what you like. If you like a low sheen, use it. If you like really shiney, glossy surfaces use High Gloss

yes match the sheen of it.

you don't have too but if you want too you could won't make it look any different realy it is all going to be finished the same way.