There is nothing horrendously complex at all about cutting rust out and stitching in new metal on old cars. Very simple in reality. Just takes time, patience, decent equipment and a bit of skill. Good fun as well!
What you really have to look out for on old cars is the standard of previous repairs. Anyone seen the Yorkshire car restorations video of Shmee150's Porsche 914? Delivered to them with what looked like good exterior bodywork but once they got to work a horror story emerges. Filler inches deep. Then it becomes difficult to repair.
Moral of the story -beware shiny paint on old cars and take a magnet with you when viewing them.