Can you mix chain link fence paint with other enamels to paint galvanized metal?

I had to strip a too dark finish off a fiberglass door using a gentle stripper, cleaning with lacquer thinner, sanded lightly with 220 paper and restaining with artist oils for a richer finish. The inside held up beautiful but the exterior peeled badly after 2 years, one door is

For example if I wanted the trim in the living room to be white but upstairs I want the trim to be a light toffee color would that be alright. Is there a rule about trim having to match?

How do I bid on a paint job?

Does the entire ceiling paint need to be removed or just the parts where its peeling off? Then what do I have to do after I remove all the paint that’s peeling?

Can you apply a drywall finish coat over latex paint?

I want to paint a previously varnished window frame, how do I go about that?

The door is stained and has a polyurethane coating. the stain has begun to wear in spots so instead of just recoating it I would like to strip it down and restain. Do I use a regular paint stripper?