As a follow centurion owner, I would highly recommend you check out oldmanmountain.com. I ended up going with the Sherpa, as my frame had no rack mounts near the dropouts, or any on the seat stay. If you have a look at the photos on this link: http://oldmanmountain.com/Pages/RackPages/RackGalleries/Pages/sherpaRear_gallery.htm - you'll notice they provide clamps to attached closer to the seat. Their quality is top-notch. At the very least, if after looking over their site, you can't find something they you think will work, I'd recommend emailing them - they were very receptive to my questions before purchasing.
Others might suggest something different, but I think you have a decent starting point with the wheels. At 36 spokes, the strength and durability are pretty much spot on. You may need to play with the gear-ratio a little. I'm not a big fan of any speeds over just one, so someone else may be able to give you a ratio that will work. Since the hub is a 12 speed, it should be fairly easy to modify it to fit what you need.
If you're concerned about the rims overall, you might want to have a go at a new rim-band, even just the rear - something with a few more inside chambers. Easiest thing to do is google either touring rims, or go to a few manufactures - Sun rim, etc. After that, just have someone with some experience lace them up with decent spokes - 14 gauge should be fine.
As for the derailleurs, you might want to take the bike to your nearest shop and have they give you a price to overhaul it. What you might not like now about the brakes, etc, could just be that the cables are old, and components themselves are in need of service. I would seek the advice of an experienced tech. They may very well be past their prime; just no sense in replacing something that really doesn't need it.
I would recommend searching through the forum for any questions about tires, or components.
The key, though, I guess is how comfortable you're going to be. There are countless suggestions that could be made, but in the end you're still going to have to pedal it; what seems right for you, may be way off for someone else.
Since you're working with a street frame I think you'll find it's going to be rock-solid. I absolutely love my centurion - even with the Pink and Yellow paint scheme...!!!...