Jason, assuming you are not going to find another cab. None close and they all have their problems.
1. Nothing in your pics is unusual. Quite typical. You will have to do a whole lot of computer searching and watching all kinds of videos to get used to techniques and how to analyze rust, cut spot welds, penetration, patch and weld and grind and fill.
2. We can't judge a repair that you say is globed with filler but still solid.
3. First rule is do not fix any more than is rusted. Do not cut out any more than is rusted except to get a better weld access or to a flange. Use only parts of a patch panel to achieve this rule. A pin hole is bigger than you think. The edges around it are real thin. Drill them to a small size that can be welded shut. 1/4 or less. This plug weld will need a copper backing to let the weld build, unless you are a real expert. The weld will not stick to the copper. If you have to make a dozen little patches or one long thin patch, that's what you have to do. (see option below)
4. If an area is bigger than the patch will reach, fabricate the rest or buy two and use some of second one to extend the first. Left over patch metal is good to use for other patching.
5. Be careful of floor repair, it will allow the cab door openings to change geometry if not braced.
6. Don't know why sandblaster left globulations.
7. You can't mig near/on braze.
8. Figuring out how and how much to repair, is an age old question all of us face all the time.
9. You need to practice up on welding thin metal before getting into this. Trying different gauge wire and settings. Then get a good feel for it. You will burn thru while patching your cab so be prepared for that.
10. Cab repair area needs to be raised high enough to sit comfortably in a roll around chair and have real good lighting. You need an angle grinder, die grinder, cutting discs, sanding discs, good air supply. Electric wire wheel or two. Copper backing material. Money.
Option to consider:
If you can stand the thought, you are not a purest and the back of patch will not be seen: If you have a rust repair where you have drilled a hole to eliminate the rust-out or you have cut out a relatively small piece, you don't have to spend all day trying to cut a piece to fit. Just cut a piece bigger than the "hole" and put it on behind as a backing plate/patch and weld it on from the front. No burn thru, no butt welding, no shadow/shrink line and easy for a beginner. This is basically a lap weld. (Most of your repairs will be butt welds.) On the back side, cover with fiber filled filler to seal, and paint. (or any other sealing method). The backside will be a raised area so, as I said, it needs to be in an area no one will see. It is, however, a solid metal fix and is nothing to be ashamed of. If the front is not filled in completely with weld, the remainder will only be .040-.050 deep, so filler it. Don't weld around the backer on the backside. Let it float. Also welding that can cause too much warpage.
I'm not talking flanging. Don't do that unless patch panels are designed for that in unseen areas.
