All,
Regarding the paddle length questions, you might want to read what I placed on the Qajaq USA website at http://www.qajaqusa.org/Equipment/paddles.html. Arm span with outstretched fingers, plus a cubit (elbow to fingertips) is a common measurement. This is just a starting point for experimentation.
I don't agree with whoever said that 85 inches was a common "limit". My main carbon expedition GP is 88 inches (I'm 5'10").
One factor that is often overlooked is that the paddle must fit both you AND the kayak you are using. Most of the sizing instructions assume you have a low-volume Greenland-style kayak. For example my expedition paddles are 88" long, 3.25" - 4" wide blades, with a 22" paddle shaft. This works great for my "Greenland-style" kayaks such as an Anas Acuta. For my Epic 18x, the foredeck is much higher, the kayak is wider, and the kayak sits much higher off the water, making it impossible to fully bury the blades, and a different paddle size is needed. I'm going to make a new GP for this kayak -- I'm still kicking around the dimensions, it will probably be 89-90 inches, 3.5 inch blade width and at least a 24 inch paddle shaft.
At the Greenland competitions, the racers prefer very sharp edges and sharp tips for speed and efficiency. Paddles built for rolling often have much more rounded edges. For a watertribe event, I'd go with very sharp edges. The trade-off is that holding the blades is not as comfortable and the sharper edges/tips are more prone to damage.
I have seen Jim's paulownia paddles and they are super-light. If anyone knows of a good source of lumber, please let me know. I usually use Western Red Cedar as it is readilly available. One trick to make the cedar tougher, when the paddle is almost finished is to take a smooth metal rod or bone, and rub it hard on the surface (this used to be a wide practice among professional baseball players with wood bats and was called "boning the bat"). This compresses the soft surface fibers and gives a little more durability. I leave the paddle "bare" or use pure tung oil to finish.
IMO, the best instructions to make a GP are Chuck Holst's, on the Qajaq USA website on the page previously mentioned.
Best,
Greg Stamer
(founder and former President of QajaqUSA)