Do it. The drive from the mainland through the entire Keys is nice. Yes, mostly 2 lane road and lots of bridges. A very long chain of coral reef islands connected by bridges. Tropical climate, lots to do. Hot a lot of the year, but during the winter months it is much better than freezing ones balls off.
Key West is cool, but I wouldn't want to live in Key West. The Keys are pricey, land is scarce and property is worth a lot. But one can still find some fairly quiet areas. I highly recommend a visit. Take several days at least, lots to do and see. You can fly in to Key West also, but I really like the drive from the mainland along the entire Keys.
Also - watch the series Bloodline on HBO. It is set in the Keys, gives you a good idea of what it is like. Great series, too.