Hi Ron!
I am so glad you are about to jump on the band wagon of biking! It's pretty much the greatest thing ever. I am a huge biker, last year when I graduated college, I was 22, I biked down the west coast, starting in Seattle and ending in San Diego!
So, If a 22 year old girl can ride a bike that far in two months, you can certainly ride a bike to work. A 12 mile round trip commute sounds like the perfect length of a commute, just enough to clear your head on the way to work, and clear your head on the way home. The busy narrow road will feel scary for the first few weeks, then it will feel like a fun adventure, and then it will be mundane like your car commute is now. Don't worry about the drivers, they can go around you.
As a former bike mechanic I recommend 2 things for new commuters. Number 1: A high quality steal frame, steal frames are indeed heavier, but they feel way safer because the vibrations on the road don't radiate through them and they don't flex like they do on aluminum or carbon do. Also, for someone of your size, the steal will make an even bigger difference, and be better for the wear on your bike. Number 2: Along those lines, get some nice tires, some commuter tires that are a little wider that stock tires, and that are 'flat-protected'. If you are worried about getting a flat, or getting stuck in tiny cracks, or rolling over bumps, your commute will be less fun. Cozy tires are great, they make the ride nice and smooth.
These two characteristics actually make 80s mountain bikes THE BEST bikes to commute on. Most 80s mountain bikes were made in America with Chromoly steal, hand welded together. You can find some really nice bikes, maybe some of the nicest for 200 bucks on Craigslist. That's just me nerd-ing out though.
Also, last tip, splurge less on the bike, and more on the all the good stuff to go with it: A super nice rain jacket, super sweet bright lights, FENDERS, a rack and a nice bag to go with it, cozy handle bars that enable you to sit up in traffic and see where you are going. These things are even more important than they bike, they are what's going to make the commute great. I also recommend going for a regular bike, upgrading to the electric once you have toned your badass bike muscles and know a little bit more about bikes.