Some warm clothing - especially full gloves, some sock liners and heavier socks, long tights and a windproof jacket and we can get you out there! (So I won't feel as alone on the bike trail). I'm in NoVA, too, and while this week is COLD (5 degrees), it'll get warm enough real soon. Many of the local shops already have their winter gear on sale, and I use a lot of cold weather gear I picked up for other reasons (e.g. not cycling specific or priced) for cold weather riding.

A cycling friend who races does some spinning and a lot of indoor trainer riding during the winter - his opinion is spinning is useful but not as cycling-specific as his longer and targeted trainer sessions. Spinning is a mix of riding, usually at an overall higher intensity, for 45 minutes-1 hour. He prefers his trainer. I see a number of people at local spinning classes who are triatheletes, so they obviously think it's helping them. I find it more enjoyable than riding a trainer by myself and the instructor and other students provides some motivation. Spinning gets the club's bike sweaty, not mine.

On the other hand, I can hit the trainer at my convenience. You can use whichever bike you want, geared or fixed. If the trainer has a means of varying resistance, it'll make riding fixed more interesting.

Spokes Etc in Vienna, per chance? I noticed their set up a few weeks ago in the back of the store. I didn't check what the story was on sessions.