Just saw this. Order of business
#1 would be to ditch the Helicomatic hub. Looks like you're on the right path with your new wheelset. Spend a little bit of time playing around with gearing at Sheldon Brown's gear calculator. See what you can set up with various triple gearing options and cassettes that could go on your new wheels. No reason why you can't cover a broad range of gearing with few (if any) dupes, and without huge gaps with some careful consideration.
I've heard shifters are a challenge to obtain presently, but I've found 9 speed cassettes and rear derailleurs to be a bit of a sweet spot for reasonable pricing, availability and gearing options. They can work with either brifters of bar-cons, or downtube shift levers. I gravitate to bar ends, but people tend to either love them or hate them.
If feel compelled to upgrade braking, Tektros are a great line and a good value and aren't in-your-face modern looking.