I've put about 50,000 miles on my carbon Trek 5200 and the frame is still perfect, though it needs a repaint. I've done everything on it, randonnees, descents down "gravel" forest service roads where the smallest rocks were the size of potatoes, double centuries, whatever. I don't treat it more carefully than any other bike. It's fallen over plenty of times, been in a few crashes. No damage to the frame or fork. And it's way stable and comfortable. It's the Ultegra version of the bike Lance won his first TdF on. Those guys aren't nuts. They want a bike that doesn't require much attention and that doesn't sap your energy. Carbon is great, as is the relaxed front end on a long distance racing bike.

I run 25c 4000s on my tandem with excellent results. We run 28c when touring loaded on it. I've run a OP rim on the tandem front, but knocked it out of true when braking/skidding in the rain and it came up hard on a dry patch. It trued up OK, though I didn't run it on the tandem again. You'll be fine with them obviously. I'm a big fan of OP Ceramic rims, which are not the same as the CD rims, very inferior. One set of those rims will last you 10s of thousands of rainy, muddy miles. I run Rolfs on the Trek, very sturdy rims, never need truing. They have lower spoke tensions than conventional wheels because of the deep section.

You can run clip-on fenders with mud extenders, which I do on the Trek.