Gaithersburg is a great area for road rides, also you can go into Rockville and pick up the Rock Creek trail and ride all the way into Georgetown.
Go to a few good bike shops and talk with them, test ride loads of bikes and see what feels good to you.

On a saturday sit in a nice spot in rock creek park with a big sign that reads "NEED BIKE ADVICE" and talk with people who stop to talk. I'm serious, people will love it and so will you.

Don't buy until you are sure what you want. Go to REI in College Park and talk bikes and clothing with them, they will talk your arm off, and they have great entry bikes with full warranty.
Have fun and enjoy the cherry blossoms.