You can paint directly over the old finish, and then cover with a clear acrylic when dry.

A word of warning; just make sure that the antique you are painting on isn't some old, valuable antique ~ once you alter the original finish, you'll lower the value significantly.

Yes, use the acrylics and then top coat with an oil based poly, preferably a wipe on poly. Zar makes a great wipe on oil based poly. Find a dealer near you. www.ugl.com/zar/...

I'd use oil paints. Most acrylics are not designed to go atop oil-based finishes. Test the dresser to find out what is on there. Denatured alcohol(found out any hardware or paint store) removes latex finishes. Dab some on a cloth and rub a test spot in a discreet spot. if the finish comes off, it's latex, if not oil-based.

I never paint over varnished furniture. I always sand it down and prime it.
The parts that get painted (if you want the best look and the best quality finish) need to be sanded, primed, painted, then sealed.
If you want the parts that you paint to have the same kind of finish (like, gloss) you can buy different sheens of sealer. There is, satin finish, semi-gloss and high-gloss. If the unpainted finished wood is not shiny at all you can wax the painted part using paste finishing wax. Minwax brand is good.