Painting - removing old trim paint

I am in the process of repainting some door/window wood trim that has already been painted at some point in the past by previous owners. It appears there are at least 2 (maybe 3) previous coats on the trim. The current paint seems to be in good shape; is not flaking or chipping or falling off.

I have no idea if the previous coats are oil or water based.

What preparation work do I need to undertake to prepare this trim to accept the new coat I paint? I plan on using water based semi-gloss on the trim.

Questions I have are:

Do I need to strip all the previous coats of paint first (this part scares me as very tedious and time consuming)?

Is a good sanding then a primer/topcoat sufficient?

Is primer even necessary?

Thanks to all for any advice and insight.

-mark-

If the paint is sound, a light sanding would take care of any rough or bumpy places. Wash with TSP, prime with Zinsser 123, then finish with a couple of coats of top quality semi-gloss.

I almost always recommend primer. Nothing like being sure that the bond is as good as it can be.

Hope this helps.

does help very much.

thank you!