+1 on getting it fit properly, particularly with back problems. Work with a good fitter, and make sure he's aware of your back issues.

As for ride comfort, once you ride it, if you find the ride jarring, put on 25, or even 28c tires (if they fit) and run lower air pressure.

As for time trialing, you'll still want to have a road bike, even if you get a dedicated TT bike down the road. And in the interim, you can put clipons on the C'dale.