The rust on the inner face of that fork leg is what I would be most concerned about as it looks to have worked in deep into the steel on the fork leg.
Don't hesitate to start taking off the finish in that area to find out how bad it is, as it could be a major riding safety concern.
of it is really bad, you might be looking at having a builder replace the fork leg or if there's just too much rust damge, replacing the whole fork.