The fact that you say you're cautious in nature is a strong point in your favor. If you haven't taken a basic motorcycle rider safety course, I'd encourage you to do so. It'll be fun, and easy for you with off road experience, but I know you'll pick up a few road riding tips that will enhance your safety.
Once that's completed, any of the late model RT's should be a good bet. They'll do everything you've listed, and have easy to modulate power. The '03 or '04 GT wouldn't be a bad choice either, except that the seating position is going to feel a bit strange to you at first, the RT will be more upright, therefore more familiar. Power wise, the '03 or '04 GT is about the same as the R1200RT, but GT is much smoother.
Once you pick out your bike, and have gotten familiar with it, I'd recommend an advanced rider course, where you ride you own bike. It'll really sharpen up your low speed handling skills.
I would NOT recommend the latest generation K bike, in the S, R, or GT version, nor any of the LT's as a first road bike. The LT can be a bit top heavy, increasing the risk of a low speed tip over, and all the new generation K bikes have pretty sensitive throttles, and spool up VERY quickly. Off road bikes get a lot of full throttle usage, just one twitch of the throttle on one of the new K bikes can get you into alarming situations in a heartbeat. Besides, the S and the new GT have a lot of fragile plastic to damage!
Good luck with your decision making, it's part of the fun.