Your thoughts are good. No one can say what is the best direction. What you are doing is actually necessary. You will gain all kinds of knowledge and experience. You can't get it from a book/internet pictures or advice from us. There are so many things involved with a restoration that doing it is the only answer. We all started where you are and are somewhere on the learning curve all the time.
Mig welding, in general, is user friendly. Use the pieces you cut off the truck to practice on. They are old metal and at the same thickness as the patches. Cut slits in them with a 1/16 wheel and weld them back up. The metal must be shinny clean on both sides of the piece. You have several processes to learn. Bracing, measuring, planning, cutting, grinding, welding, fixing blow thru, welder adjustments. It is a hobby and it is fun.........some days it's not fun until you get re-motivated, that's natural. Having something to do in retirement is exactly why I am doing it. You have no schedule, no boss, no hurry.
One of the mistakes newbees make is buying a whole bunch of stuff to get ready for the "rebuild". Wait until you are ready for an area, then buy. It only takes a few days now to get parts delivered. Stacking them all up and storing them, then losing interest or health problems, etc......is why there are so many basket cases for sale. Somehow, buying a bunch of parts makes some folks think they are restoring. Meanwhile the rust and mice eat it all up
Go for it. Now that you have made the decision, no more advice as to direction from us. Now just post your questions in the appropriate forum if you get stuck on something........anything.
I know you just asked for sequence, but is was good to brainstorm the overall cab. There is no sequence, as you have said. Just trying to keep the doors fitting and the cab in general shape. I know you get the picture. If something gets out of whack, just try to catch it and re-support. Prop it, jack it, brace it, bolt it, clamp it, lever it........whatever. Like you said: Use clamps and self tapping screws to mock it up and examine your progress. You can, for sure, tack weld it yourself when satisfied, then move to the next patch, as you also said. Knowing that you can reposition what you already did if necessary.
