If it were mine, the first thing I'd do would be to strip it down to the frame, get everything cleaned up, fresh cables/housings, new brake pads, new chain plus an evaluation of the chainrings and freewheel for wear. A quick rebuild of the derailleur pulleys and possibly brakes...
Then I'd put her back together with fresh grease, oil, and handlebar tape, and go for a nice, long ride.

Enjoy it!