Sheldon is a good resource, particularly on old bikes. I'm not sure he has a start to finish guide, but just search whatever part you are working on at the time.
http://www.sheldonbrown.com/
And youtube. Pick a thing to work on, and google it. Nothing is to hard to DIY on a bike like that.
Multi vs single will entirely depend on where you want to ride, hills, and your strength and desire to suffer if you have climbs. If it is for commuting, put your road bike in one gear you feel comfortable in, and see if you would like to do your commute in that gear, every day.