I'm running 32h dyads with similar spokes, I probably weigh as much as you and your bags and the wheel hasn't needed any adjustment now in its second year. I've used the bike on entry level MTB trails and last year loaded it for a few hundred miles with a trailer and bags. Things are moving away from more spokes as the quality of spokes has improved and the strength of rims has really gone up. How old is your Kuwahara? You mention 7sp which would be 127mm, stretching to 135mm even on a steel bike is something I really wouldn't want to do. If I was worried about strength and sticking with 7 speed I would consider getting an axle for a 130mm road hub and adding 3mm to the non-drive side only, it won't completely make the difference but by moving the rim over the difference it will help to balance spoke tension and make a stronger build.