well, I do not really see a point in sanding down to the metal unless you have to. I pretty much grew up in a paint booth so I've got a lot of experience in the what to do/not to do dept.
I would sand the entire car especially any areas that are pitted, making them nice and flat. A light coat of primer just to get the idea of problem areas, and then wet sand the whole car, then prep for paint.
I've painted my bird several times now and find it necessary to remove the front, rear lights, both mirrors and the deck lid...but my car was only painted pearl white from the original color, so for the door jams and all that, all I had to do was remove any dirt/wax from those area, scotch brite the hell out it then cleaned and shot it. Anyone will paint anything, for a price. Getting into door jams and what not take more work so thats means more $$$. If your changing the color, it would be wise to remove everything possible, even glass to properly get it done. Nothing looks worse than a car that was repainted and did a half ass job doing it. Pretty much your looking at taking off everything. A lot of work but worth it to get it done right.
I will be actually painting my car (again) in two weeks so I will post up a lot of how-to pictures. I'm only doing pearl white with some sort of pearl ghost flames is what I'm shooting for at the moment.