re noodly, I bought a kuwahara in 90 or 91, (still own it) and toured on it a bunch of times. Your frame is older, may be diff tubing, plus its bigger (less stiff?), but mine was a little flexy when riding standing up, but I really only noticed how flexy when decades later I got a new tourer, and noticed how much stiffer the new bike was--but that said, I rode that bike loaded a fair amount and had a great time on my trips, so you'll just have to see how it is.
re racks, my feeling is that a stiffer rack front or back will help how a bike feels riding.
re gearing, yours is a 6 speed right? Mine was 7 and so you could lookk into the rear wheel spacing , probably 126mm, and see if its a freewheel or a cassette, and what 7 speed stuff you can put on it, or even if you can go to 8. Given that you'll be buying trigger shifters anyway, go as high as you can, if 8 great, if 7 then thats what it is.
butterfly bars work well, I like them, and while I dont really get the need to do the double brake lever tihng, try it and see, personally I really dont see the need at all. I ride a commuter with these bars and its fine with the mtn bike brake levers only and 7 spped trigger shifters.