Keep in mind that it is 40 years old. Any point of failure, electrical (make sure all connections are in good repair, we have all heard the electric horror stories on bikes), wheel bearings (if original replace with new bearings), Tires make them new (check date code on side wall).
Creature features you are on your own. 754 hit it on the head find the running sweet spot. I would look for some type of throttle lock (just to give the old hand a break), bars, seats, highway pegs, etc. everyone has an opinion and everyone is different). A fairing is nice for those crappy weather days, but then so is good riding gear. Storage, where do you put all of you crap. There is a lot of good weather proof bags available today that can be put on, although typically not cheap.
I have several bikes, older and newer, somehow I have set them up all to be similar in riding position. So going from one to another is an easy transition. Seats are always an issue even on new bikes. Maybe look at a strap on type, Airhawk or some type of gel pad.