It is just a rough estimate, but when I ride on tour I run the granny and middle most of the time, and when I am at home without the load, I ride the middle and large chainrings. So there is a full chaining difference in running loaded. That would have to be reflectied somehow in the gearing choice for the single speed.
1) Touring on a single speed is OK, but: There certainly are disadvantages: loss of gearing choices;
2) There is a big difference between choosing as a challenge thing to go singlespeed, and making do. I have lived places where people predominantly rode single speed due to era or poverty, and they walk up hills. Personally I would minimally add a rear wheel and shifter.