I have used both new and repop parts on my truck. If it is possible for me to repair it or find a used replacement in better shape, I will. Some things such as floor pans, rockers, and other patch pieces are much easier to buy and tweak a little to make work than to find solid used replacements. How many times have you seen one of our trucks that doesn't have rusty cab corners? Not much.
On the other hand, I will look high and low to find a good fender, or core support, etc. than to buy a repop. Most just don't fit without a lot of work.
I am over 60 and I have been working on mine for a couple of years now and I am really enjoying the patching and fitting of the panels I need to replace. It's good therapy and I get a real sense of accomplishment when I can fix a floor panel or whatever and then look at it and say "I did this myself".
I do miss having the truck to drive while I work on it and for some this can be very discouraging because it is definitely a long term commitment to take the time to do your own rust repair.
The main thing is to just make sure you are having fun whatever direction to choose to go.