Hi again,
You will enjoy touring on your proposed Thorn bike. They do seem to have it worked out.
I use mine for short tours, but I go with all I need for camping and have carried up to 25kgs of load.
I find my Thorn bike handles really nicely when laden. I did try a handlebar bag, but loaded it gave me a funny effect on the feel of the handlebars and I stopped using it. I now use 4 panniers, a stuff sack on top of the rear rack, 3 drink bottles and a small cape roll size bag which I velcro under the top tube for easy access to money etc.
I have a dynohub and leave a lighting system fitted all year. I use a Rohloff hub and have found the most useful features to be the even gear spacing, the ability to stop and then change gear whilst stationary and the straight chain line reducing wear by an incredible amount compared to previous derailleur systems.
The bike has needed very little maintenance and has had the brake pads changed once in 4k miles. I have never had to use the tools and spares which I carry except for an early use of Panaracer Tourguards being damaged by glass. I changed to Schwalbe XRs and have had no noticeable damage since then, although the ride is not as supple as a lighter tyre.
You have a nice task deciding just what tyres to ride on, not to mention the other items you will need to kit your bike out with for expedition touring.
Julian.