I'm new to paint/body work and I'm trying to restore this fender. I've removed most of the dings/dents, but I'm not sure what the best way would be to proceed.

A) Strip it to bare metal with a paint stripper
B) Sand it down to the primer

I did spray a coat of paint stripper on but it only took off the clear and maybe some of the top layer.

There's only one bare metal spot, where the rust is. Do you think it's necessary to strip this fender down to bare metal?

 

more pics

 

if you get some sandpaper that is course enough to take off paint but not groove metal real deep you can just sand it down.

 

If it was me I would. That fender has been painted more than once and the paint that is on it is really rough looking. I don't know if your restoring your car or just doing a quick fix? I would strip it to bare metal, do your metal work, spray it with epoxy primer, filler on repair areas and block sand, spray with a filler primer, block sand the fender and paint it.

 

Strip it. Do what TEEZER said. No questions asked. I did that to my whole car that was in way better condition than that fender. Aircraft stripper. Apply, let sit, scrape, repeat.

 

Either with stripper or 40 grit, get ALL the paint off. Usually you can just sand down to the primer if it's in decent shape, but because you have already used stripper, the integrity of all the paint is compromised! get it off.
I prefer sanding because I get to explore the surface and find all the low and high spots. Saves having to use an etcher as well as the metal will be nice and etched by the 40/80 grit sand paper. If you don't have good sander tools, use the stripper.