Removing the rear rotors isn't hard. If a previous owner never took them off, they will be riveted on, so you may have to drill the rivets out. Ensure that you index the rotors with respect to the lugs so that you put them on exactly the way they came off - ie. the same lug in the same hole on the rotor. This is important on a car with fixed calipers like the C3s in order to preserve the runout measurement within specifications.
99% of C3 owners have the trailing arms professionally rebuilt due to the tools and knowledge required to set up the rear wheel bearings correctly. Ask around here and someone can recommend a good place to have them done.
Do some searches here on CAC for rear wheel bearings and for C3 brakes in general - they are different from the floating caliper systems found on most cars. Don't have your rotors turned unless they REALLY need it - and then, take the time to find a shop that can turn them on the car.