Yes, you can, the base is similar.
you can paint over latex paint with latex enamel.
Enamel is a word used to describe a finish, not the formulation of a paint. It simply means a hard reflective surface. Many people mistakenly use the word enamel when referring to oil based paints. So. if you are asking if you can paint latex or acrylic paint over a latex or acrylic enamel the answer is yes, however, I strongly recommend you sand the old paint first to give the top coat "tooth". If you are asking about painting latex or acrylic over an oil based paint the answer is still yes, however you must first sand the old paint and apply a good quality primer to it. Check with a reputable paint retailer for the best brand in your area.
No, it will not stick properly.
Yes, enamel paint will go over flat paint.
Not directly. You will need to use a primer made to adhere to oil and will accept a latex topcoat.
You can in some cses, but Minwax does not reccomend it.
You can apply "oil" based polyurethane over "oil" based enamel, you can also apply "water" based polyurethane over "water" based enamel, never mix the two, there's to much of a chance for problems.
You can use either enamel (oil-based) paint or latex (water-based) paint. If you are using latex paint, you need to use a primer (undercoat) first. The paint store will have a special primer that allows you to paint latex over enamel. If you are going to do this, it is also a good idea to either sand the enamel paint before you paint over it, or wash it with TSP (trisodium phosphate) cleaner to remove the gloss.
It will protect the paint as long as you use a water based varnish, never use oil based varnish over water based paint. Tip: "water based enamel= water based finish". "oil based enamel= oil based finish".
If you are painting a residence the chances are your enamel is a water borne acrylic enamel. Conversely, if you are referring to acrylic and enamel spray cans then the answer is yes you can spray one to another without any problems. Always be sure your paint is completely dry before applying successive coats.
Lacquer can cause the paint to bubble or crack due to the very hot solvent that is a part of lacquer. If you want a clear coat over paint, a better choice is spar varnish over oil base paint and arcylic urethane over latex.
If the base coat used in your project is water base then yes, you bet you can. If there is any chance that the base coat used was an oil base paint then you cannot paint directly over it. The acrylic enamel will not adhere to the oil base paint and will begin to peel off as soon as it is dry. In which case a coat of primer is in order.