Tim:
Poke around the floor especially near the utility doors and windows. You will have a lot of work if the flooring needs to be replaced. Make sure the plumbing can hold pressure. Have the seller fill the water tank and then test the pump. Check out the refrigerator. Have him fire it up before you get there....it may take the old propane types more than 12 hours to cool down. Replacing the frig is expensive....starting at $700-800. The broken heater (I assume you mean furnace, not hot water) will probably need to be replaced with a newer model and fitting it into the existing space may prove difficult without reworking of cabinetry.
As far as the running gear: axle, tires, brakes and connector: I'd make sure they are all functional before driving it any significant distance. I was VERY lucky when I towed my rig 1,000 miles with bad tires and no brakes. I'm much wiser now!
Hope this helps. Good luck and enjoy the adventure.
Jeff
1968 Caravel