Need help with purchas of 68 Dart!

Anything can be fixed including rusted frame rails. For learning, worse shape the better ?
Probably not. Just depends on how much you want to learn and how much workspace you have. Grinding and welding, painting, engine building, upholstery, can all be done in one small workspace but it aint easy. A lot of time will be spent just moving things around. Lots of tools needed too.
As for what vehicle so much time and money is invested in, Everyone has their own likes and dislikes.