Regarding weight of the bike versus weight of the frame, I forgot to weigh the frame and fork before I built up my bike. At that time they did not list frame and fork weight anywhere, so I had no data on that. I weighed a bunch of the other parts, but thanks to a Windows update, I no longer have the software to read that data, thus all I can say is what my bike with all the components weighs. And when you are building up a bike to carry a load, you do not want to use lighter components that might be too weak, so I did not consider weight when comparing the components that I was using to build it up. Thus, I have some heavier components.
I tried a Tubus Tara on my Nomad, the horizontal bar was pretty far from horizontal, so I did not use it, used a different rack.
I commented above that:
Nomad is rated for something like 60kg of gear not counting weight of rider. That is a LOT of stuff. Bike unladen is roughly 20kg, which is pretty heavy for a bike.
I have not looked at a brochure on Thorn bikes for a few years. When I bought my Nomad frame in late winter/early spring 2013, the brochure had a table of data on each frame size, I did a screen print of that table and attached it. This was from the sales brochure for the Nomad dated Autumn 2012. I have the size 590M. Thus, with four panniers, handlebar bag and three water cages, the table lists capacity (assuming distributed properly) at 62 kg.
If they have changed the rated weight capacity, I am unaware of such a change. There was a comment above about the X frames, they are listed in the table too, if they have anymore X frames and if you are interested in it, this provides some data.
That table might have an error in the size you are looking at, the 565M, the chainstay length on the table looks wrong to me, as they list it shorter than the 540L. I suggest you get your data from the current brochure.
I have tried my shifter in at least three different locations. When I was going up hill on some difficult terrain on a cobbley road in Iceland, there were several times that I wished I could have taken one hand off of the handlebars to reach the the shifter to change gears, the shifter at that time was close to where you would have it if you use the 55mm accessory bar. But the terrain was so difficult that I could not take a hand of the handlebar to reach over to where I had the shifter, which was inconvenient.
I have several derailleur bikes with bar end shifters, I first used bar end shifters in the 1980s, so I am used to reaching to the end of the handlebar to shift. When I got home from that trip I decided to use the Hubbub Adapter to mount my shifter on the end of the handlebars, thus I can have both hands near the ends of the bars for better leverage when steering in difficult terrain and one of those hands can be on the shifter. I am very happy with this location. I routed my cables differently than most people, I used some V brake noodles to orient the cables further forward. Two photos attached. But as I mentioned, for decades I have reached to that location on other bikes to shift so it made sense for me to use that option. If you have never used bar end shifters, you might not like that shifter location.