Re: door painting issues
You should be able to paint the interior side of the door with relative ease, but you've got to make sure that your primer and top coat are going to stick to whatever the finish is that's already on the door. Do a test, with both the primer AND with paint over primer and see how it adheres.
1 - Start with a TSP wash of the interior side of the door, this will clean and etch the surface ready to accept the primer.
2 - Prime with Zinnser Bull's Eye 123 or with Kilz original primer. Bull's eye is a latex base, Kilz is an oil base.
3 - Choose a good brand of paint for your top coat. I prefer Kelly Moore, but any of the name brand paint dealers will suffice. I have yet to use a Behr product that cures or sticks or even applies well, so I never recommend those, however, there are those here that swear by the brand. Your mileage may vary.
Once you've done your test, prime the entire door with two coats, followed by two coats of paint. Be sure to remove the doorknob and any other hardware on the door, but leave it on the hinge, as it will be easiest to work with in place. Just don't paint or slop paint all over the hinges. Use a good quality brush, such as a Purdy or Baker brand.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!