You are right that a frame gets a lot of stress from a disc brake. But the Nomad frame which can take the stress of a Rohloff on the dropout should be able to take the stress. Don't worry about it.
If you put a disc on the rear and use V brake on the front, you might consider switching your CSS rim to the front - but that would only work if both front and rear have the same number of spoke holes.
I use V brakes on my Nomad, so I can't comment on fitting of a rack on the Nomad with a disc. But I use a disc (TRP Spyre) in the rear on my Lynskey Backroad (a titanium derailleur fitted touring bike) and a V brake (with Koolstop Salmon pads) on the front. Thus, with both a V brake and disc brake on the same bike I can compare them. (Simpson also has both types on one bike, as he noted.) I find that the V brake in dry conditions seems to work a little better than the disc brake, but in wet conditions the disc brake is clearly better. On that bike, my rim brake is not on a CSS rim.
The Spyre instructions recommended compressionless housing, which I used for most of my cable run. I do not know if that is important or not, but I think that my brake action feels better than it would otherwise if I did not use compressionless housing. Note that brake cable housing that is compressionless is different than shifter compressionless housing. You cannot use shifter housing for braking, you must use brake housing.
I have never used any disc other than the TRP Spyre, so I can't compare. But I think that the TRP mechanical brakes that actuate a pad from both sides instead the disc brake units that actuate only one side make a lot of sense. Last month I was on a trip and someone had problems with her non-TRP brake. I tried to adjust it so that it did not rub, it would have been a lot easier to adjust her brake if she had a TRP.
The photo is of my Spyre on my Lynskey. It is mounted on the chainstay, not the seatstay like on the Nomad. Thus, I have no clue if your rack would fit with that brake or not. And if you could put both the brake and rack on the bike, would the rack interfere with your ability to adjust the brake?