Yes, it will.
Yes, you can generally paint high gloss latex over flat latex paint. But you must do all the preparation work in the best tradition of any professional painter. All "flaking" must be removed and the raw wood primed. This will present a "smooth" surface for the new coating. Additionally, everything that is to be painted my be scrupulously clean and free of anything that will restrict the new latex from sticking to the old.
Most glues will stick to gloss paint.
Latex paint can stick to the floor grouting.
no it will not stick
The only way to prevent scratches and skuffs on a latex surface is to be carefull what you set on it or put against it. Consider using a lower gloss paint rather than a high gloss as marks on high gloss stand out more. If you want to prevent scratches on a horizontal surface, place glass or a sheet of plastic over it. However, you'll need small pads on the corners so that the air can circulate between the table and the glass. Otherwise, the paint may stick.
Clear primer.
Not if the melamine paint is oil (alkyd) based.
It will not stick very well unless you use a primer in between.
The flat latex paint will stick to satin or semi-gloss latex paint without any problems. The main consern is making sure the surface is clean and sound before begining to paint, plus use top quality paints for the best results.
I wouldn't recommend it. Some of the chemicals in the alkyd will dissolve the latex and the alkyd won't "stick". It's best to remove the latex using laquer thinner or xylene first.
Yes, but you should clean and lightly sand the gloss paint first, to give the new paint a good 'key' surface. Cleaning can be done with a degreasing agent such as 'sugar soap', following the instructions thoroughly before applying the new paint.
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.