Here's the strategy I'd use:

Read up on bike fit and run some online calculators to narrow down the size bike you want.

Visit Craigslist every morning, and if you find something that looks good, post a link to it here and ask for advice. For older bikes, the Classic and Vintage forum might be best. Like this. Or this.

It would be best if you have a friend who knows bikes to go with you.

Take a helmet when you go for a test drive, since falling is more likely when riding a strange new bike.

You might buy a bike, use it to refine what it is you want, then sell it and buy another.

Good luck, have fun!