Here's a couple suggestions:
1. As people said before, start easy--great weather, once a week. Do it for a month then ramp up. I stopped biking for 10 years and was gasping for breath when I started back up. Within a year, it was no longer a workout. Start somewhere where there's not a lot of traffic if you can, and maybe start just on a weekend. I find weekend traffic to be much less than commuter traffic, so good to practice in if you're not an experienced biker.
2. If you don't want to do freezing weather, don't. Don't feel bad about skipping the rain. It damages the bike and you'll have to change clothes at work. I love biking, and before I had kids, I used to bike in freezing weather. It's freezes your eyes and cheeks--I finally got a snowboarding helmet to keep my ears warm.
3. Buy a cheap but functional bike off of craigslist that has multiple gears. Then once you've gotten experience with it, you'll know better what you like. If you haven't had an accident, you can sell it for what you bought it for after a couple of months.