I'm about to the roadworthy stage of my 2nd resto-rat. I'd suggest taking a close look at your wallet, your calendar and your heart. Both of mine took more money and time than I had planned on, by orders of magnitue. When all is spent and done, you still have a 30-year old bike, even if you have it performing better than stock. If your heart is still good with that, then proceed. In general, try to get one as complete and in as good of condition as possible. It will most likely be cheaper in the long run.
Enjoy. There is something really satisfying in bringing an old abandoned/neglected bike back to life.