Didn't read everything above but if you're starting from scratch there's every reason to build a freehub instead of a freewheel hub. You can go with Uniglide flavour, Hyperglide flavour, or some Frankenfreehub depending on your goals and willingness to customize. Considering your 126mm constraint, I suspect Uniglide gives you the best starting point in terms of hub availability, but I guess there are many ways to get a HG hub to work in a 126mm OLD setup if that's your goal.
Either way, sprocket availability will not be an issue in the foreseable future, as HG sprockets are easily adapted to UG splines.
BTW, I'm more or less average in weight, but somehow I've managed to bend or tweak at least 2 freewheel axles while riding, both 120-124mm OLD, give or take.