Thanks guys! Just what I was looking for.....I did say 1/8" in the first post, but the rib gussets are actually 1/16"!! All 900+ of them...

The dremel saw blade jewller blade idea sounds the best to me - I have tried the snips method and found it crushed and split too much - maybe not the right snips.....and I am cutting sheets that are 1.2m square (about 47 inches square) to start, so the mitre box won't work, I don't think.

I will look for a bandsaw - the blade will need 32 teeth per inch for 1/16" ply - if they come that fine.
Routing around those 900 tiny little 1/16" ply gussets might take a while.......and a few cutters.......
Thanks again for the suggestions - it has helped a lot!! Mark