I'd start by giving everything a very thorough cleaning. Don't leave any bit untouched. I assume you want to keep it as original as possible so I would be reluctant to replace things that are part of the bike's original character. I expect a bike of this age needs to have all the bearings checked, cleaned re-greased. This is something you may want your LBS to do as it requires some specialized tools and experience. Have them check the chain length while you're there to see if there is any stretch. If the cables work fine and there is no rust, then I'd leave them alone. If not, you may want to replace the cables. The housing may or may not need replacing, but if find you need to replace the cables, then replace both cables and housing. Maybe put fresh bar tape on it.