I used 3/4" for the top of my benchwork. The more solid the structure is, the less the vibrations, hence....."Quieter". For what it cost's to go to 3/4" I would go that way.
I also used a gasket between wherever the table top and the substructure touched. I used the stuff you can buy in a roll at the lumber yards, I think it's called "sill gasket". Really don't know how much it helped, but seemed like a good idea at the time. I'm sure it helps a bit.
The other thing I did, was to cover the whole table top with hardwood floor underlay pad. The stuff is about 3/16" thick, sort of a harder compound than regular carpet underlay, and a little thinner. This has worked great. I use all fastrack, which is noted for being noisey, but with my set up, I'm very happy with the noise level. I don't notice it at all.
As far as height, I have a 2 level deal, where the 1st level is at 36", and the top is at 42". You will get all kinds of suggestions as to what folks prefer. Some prefer higher so it's easier to crawl around under it, and some like lower, for a sort of ariel type view. Just depends on your own preferences. I'm about 6' tall, and I wouldn't want my upper level to higher than 42", but that's just my preference.
Just a little food for thought, hope it helps. If you are looking to minimize the noise, the best place to start is right at the beginning. Every little bit helps, and a lot easier to do in the beginning.
REV