The only other issues I've had with my E36 have been the hood release cable breaking and a door actuator going bad. The hood release cable breaking is common if you don't properly grease the latches once in a while. I got lucky and the cable itself didn't break just the latch attached to the kick panel and I had to start using vice grips to open it. The dealership charges $900 to fix it claiming they have to remove the fender. You don't, at all. Theirs a great writeup on how to fix it already and the cable is a $40 part. The door actuator has micro switches in then and eventually they stop making contact and of course stop working causeing issues with the Central Locking System. A new actuator is about $75-80. Not super hard to replace just got to take the door panel off. Those ate really the only major issues I've had thankfully.
Front fenders are easy to replace. Just take one off a car in a junkyard. Places near the ocean or use salt for road de icing will have higher concentrations of rust. Swapping a front fender is easy. Just check local junkyards for the cheapest option.
And yes you are correct. When you say begun restoration how much work is required?