You may want to consider Hawaiian Koa. Very light and resonate wood. Contact Jude Moreau a few years he built a Koa accordion now owned by a musician in the Bay Area. The box is very lightweight and sounds very good. Jude is very capable and can use a variety of techniques to give you exactly what you want.
I tried on this summer and yes, it was the lightest Cajun box I had ever lifted or played.. pototao chip light. I don't know about the resonance or projection.. I did sense that there was less volume, but hardly noticeable if weight is your priority.
Nice soundbites on your sight ! IF you are in Austin you might know BJ Williams who plays cajun accordion with the Gulf Coast Playboys.. he plays Jude's accordions and may be able to give insights.
Good luck..and go with the Koa ! Glenn ( it's pretty too )
The wood was very light, but I'm not so certain about the reedplates on the old boxes -- I think they tend to be heavy, however, not heavy enough to offset the lightness of the wood.
Also, I've played a few of the classic old Hebert black boxes, the funky ones with Hohner hardware, and they were very very light.
I've heard from many people that the wood the accordion's made of makes no difference in the sound of the accordion, it's all in how the reeds are tuned and possibly the wood block that the reed plates sit in.
I'd say be careful of what wood you choose, idealy it should be sturdy wood, whatever you decide.
There are sturdy light woods out there, I just don't know of any. I'm not very familiar with alot of wood. It seems alot of the lightest popular woods are about 7 or 8 pounds (I forget which) per accordion.
I was gonna prank call a builder and say that I want one made of "Charles wood." However, I don't think they'd find any humor in it though!
Italian makers will beg to differ and claim wood quality does influence tone quality. They are convinced Olive is the loudest wood and I tend to agree after trying one.