Yes, after allowing a sufficient time for the base to dry.
yes but you cannot put latex on top of oil based surfaces You actually are NOT advised to put oil over latex surfaces, which is why you're supposed to prime will an oil-based (alkyd) primer. Latex and Polyurethane should always have a layer of oil-base beneath it.
No, it's not a latex base.
Yes, you can.
Can you restate your question are you asking what is the latex paint or are you asking when was the invention of the latex paint.
Just paint it on if the latex is adhering well.
I'm not an expert, but if you paint the gloss paint with flat paint or primer and then rough the paint or scratch grooves in the paint your plaster should stick. Your grooves might need to be fairly deep. Not so deep as to go through the original plaster or drywall (depending on the original surface), but as deep as you can go. A cross-hatching pattern would probably be best. You may have to sand the paint off. I have gotten lucky in the past and have not had to.
You can always paint latex ( water based )over an oil based paint as the latex just dries on the surface. However don't paint an oil based over a latex paint. Oil based paints need to absorb into the wood or other surfaces or it will just dry and flake off. For more information on the differences and when or not to use a latex or oil paint please see the following article. . http://www.ehow.com/how_4713170_between-latex-oil-base-paint.html
Yes, as long as the polyurethane is oil-based.
no it will not stick
Yes, just ensure that the surface is clean, grease free and dulled.
No, they will not mix,
No, you either need to really rough up the oil paint with fine sand paper, or put a base coat on before you paint with your Latex paint. If you don't your Latex paint won't adhere.