I'd go with a 36 spoke wheel, X3 or 4, with right-side spokes one gauge heavier than the rest and carry a FW tool. Build the wheel well. Use a proven hub. Shimano, Phi Wood or the like. Grease the hub threads well with lots quality (Phil Wood or equiv.) grease. If you are really paranoid, bring the smallest crescent wrench that will open to fit the FW tool. You will need to find a pipe and your wrench will be trash after but it will work.
I cannot claim long tours, just a few solo tours (Boston to Detroit, Minneapolis to Saginaw Michigan) but I did those in the '70s long before cassettes. Never had an issue with spokes.
If you mix Italian and Japanese hubs and freewheels, ride that combo first, then take off the FW, re-grease and re-install BEFORE you leave. Italian threads were (are?) cut and Japanese threads were and are rolled, The first time you mix them, you are forcing the peaks of the Italian threads down to the rolled rounds of the Japanese threads. It's a hard install and even harder removal. You want full shop tools that first time. After that, your Italian threads are "rolled" and you won't have further issues. (I've put many SunTour FWs on Campagnolo hubs.)
Ben