I have only broken spokes on wheels from a 1960s vintage bike. I have never broken a spoke on a wheel that I built.
That said, I carry spare spokes on a tour.
Exception, I did not build the wheels on my road bike, thus I did not know the spoke length, instead I bought a Fiber Fix Emergency Spoke. Ph included a link in his post on where to buy in UK. I have never toured with that bike, but I thought it would be a good idea to carry a fiber fix spoke on a brevet or if I ever use that bike for a credit card tour.
More spokes makes it less likely you will break a spoke. I have carried heavy loads on my 36 spoke wheels, it is unlikely you will benefit much if you had more. That said, Co-Motion, a bike builder in USA makes the Americano which is a solo touring bike, the non-Rohloff version of that bike uses tandem wheels that are 40 spoke. In my opinion the 40 spoke wheels are less important than the tandem rear hub, that is used to build an undished rear wheel. That is the strongest rear wheel I have seen on a derailleur touring bike.
And speaking of dish, there is a reason most touring bikes are built with 135mm rear hubs instead of 130, there is less dish that way. This paragraph shows my ignorance of the newer bikes with thru axle, I have no clue about those wheels.
When I tour on a derailleur fitted bike, I carry the tools to unthread a cassette lock ring. But only once needed to use those tools on a tour.
You are over-thinking this.