Owner/builder here, of a 1939 home. I invested in a home reference library part way through my own improvements; I should have done it before even lifting a screwdriver. Renovations (https://www.bookfinder.com/search_s/?title=Renovation%205th%...), from Taunton Press, is the first source I consult when starting a home improvement project. Chapter 18 is all about painting. Many of the other titles from Taunton are excellent, but Renovations is unmatched in it's coverage.

All of the flat white MDF trim you buy is primed and ready for painting, too.