Hello and welcome!
Both cars you mention sound fine choices.
Now, bodywork...
Firstly, I think I am on safe ground when I say that all repair panels are now available (from the club) to deal with the really common areas, GRP replacement panels are also available for the front end (which is the place where the cars suffer the most), these panels are of extremely good quality. They (along with the repair panels) are available to club members.
Places to look for rust is:
Sills.
Door bottoms (particualry the rear doors).
Chassis rails (you need to remove the front wheels to examine these properly).
Boot floor.
Lip of both the bonnet (leading edge) and the boot's vertical panel (where the lock is).
Windscreen corners.
The vent panel (above the rear screen).
But that said rust can break out anywhere, take a magnet to check for filler.
New NOS metal panels are becoming very rare (and very expensive), Also on the rare list is the interior seat coverings so please check the seats are in good order (especially the back of the rear seat as this is very prone to sun damage).
I am sure there is something I have missed, so if anyone could add anything else please?