Do I need to sand or is a good wash down enough? Or maybe a liquid
sander?
A good wash, followed by a thorough drying, followed by a light sanding with fine grit sand paper to rough up the existing surface. Sanding ensures the new paint will get a good grip on the old paint.
Do I need to prime, or is the old paint (cleaned a bit) good enough?
No, its been sealed long ago - just clean and sand.
Is there any special paint, other than exterior trim (probably satin
or semigloss) to consider?
Since there's already latex on it, exterior latex should be fine.
Is there any additive I should use with the paint for flow, finish,
hardness?
No.
Do I really need more than 2 coats?
If it were white over black- you might need 3. Black over white, you might only need one good thick coat.
Is there something else I am failing to ask/think about?
Get saw-horses. Lay door flat on saw horses. Remove door from hinges, remove all hardware, tape all glass. Paint ONE SIDE only at a time, let try completely, then paint other side.
There are two critical steps in prepping kitchen walls.
Clean and degloss
Cleaning is critical: TSP or TSP substitute.
Deglossing: either light sanding (120 grit) or a chemical deglosser
Once a surface is deglossed, it should be primed, especially if going from one paint type to another.
A deglossed oil undercoat can be primed with a latex primer. Either oil or latex can then be used as a topcoat.
A deglossed oil undercoat can be primed with a oil primer. Either oil or latex can then be used as a topcoat.
It is better to stick within families of paint types, if you can, but going back and forth between types is possible with primers.
At this stage in coating, I'd let everything dry for a week, then sand lightly. If the previous layers are adhering, then proceed with latex primer, latex topcoat.
If,, however, they are sloughing or chipping or you can easily pull a layer off if you leave painters tape on overnight (and then pull it off), then you must sand down to the last well adhered layer and then repaint. Good luck.
Best Answer
I wouldn't use oil-based paint. More expensive and harder to clean up. I'd use acrylic latex (water-based) paint. No primer is required. Make sure the door is clean, (I.e.: no oil, grease, crayon marks, etc.). Quick drying and easy clean up.