Welcome to the forum
Too bad that you have that much rust to deal with. It is all repairable if you have the ambition to tackle a project that big. Pretty much all the repair panels you need are available. The rust in the top of the cab is probably the most difficult to repair. I have to agree that if you can find a better cab, that might be a better option. In the mean time try and clean out behind all the areas where there is rust appearing. There are plastic plugs in the ends of the rocker panels that will allow access to the inside of them. high pressure water works good for that as well as other areas. Cleaning those areas out will slow the rust progression a little.