Nix the belt sander. Too great a possibility of harming the surface. A vibrating disk sander would be the best tool after the major amount of paint is gone and the surface dried. You may be able to dry-sand to satisfaction if the paint is not peeling. Otherwise, you have to get all the loose or damaged paint out of the way.
Get a chemical stripper-yes be careful, follow directions, etc. Most of the really *good* ones have been either watered down or banned. Water-based solutions can work well, depending on the coating being removed.
Be ready for a liquid mess, get some chemical gloves and steel wool and a respirator/mask. Work with your surface horizontally if you can.
Follow directions but generally, you paint on the stripper, let stand a few moments, wipe off-you can use a wet towel and wring it out in a bucket with the water-based versions. The steel wool can help break up the loosening paint but let the stripper do the work.
Rinse, repeat. Until you get where you want to be, each application will do a lot or a little depending how much paint is there.
At some point it will be solid enough for finish sanding. Let dry thoroughly. The dust from that is probably worse than the stripper fumes so take precautions.
I would use 150 sandpaper and finish with 220 or better. A vibrating disk sander is very forgiving, just keep it moving. Consider priming after this process. You may want to sand again (and again) after priming if the finish is less than perfect. Have your primer tinted toward the color you will end up with. Example: Prime with dark gray if your final coating is black.