If it is just surface rust that needs to be fixed, I would just grind it down provided there is still a good amount of metal there and use a thin coat of good quality body filler to smooth it out. I'm leaving a few important steps out here ;)
I would say if theres any holes, that yeah you probably want to have them cut out and a new piece welded inplace, but I don't think any of your rust is that bad.
I would say if theres any holes, that yeah you probably want to have them cut out and a new piece welded inplace, but I don't think any of your rust is that bad.