The first thing you do is ensure the bike is safe to ride and then ride it for the better part of a season. Once you and the bike get to know each other, then you consider spending big bucks to make it the way you want it.

Also, get to know how to maintain your bicycle, as others have suggested. And you will be surprised how easy it is to learn to do many fundamental tasks.

And, if the interest is there, spend some time learning about vintage bicycles. I publish MY "TEN SPEEDS", a website intended to help people, new to the vintage bicycle interest, get a head start on learning about them.

And lastly, from me anyway, have a look at my Cannondale400, which I rode quite a bit a few years ago...