Hey Erez, wow a take a part! when I built a Coho I used 4oz s-glass in all kinds of places, for a big boat it came out really light. I think the boat is a great design,,but I made it for a 150lb guy and he rarely uses it in his biz, he can't get a comfortable grip for his thighs, I've still got to retro-fit some thigh braces. The WR isn't as roomy and the keyhole cockpit provides a more secure grip with thigh braces glued it.
I think the Merganser hits the mark for a medium displacement kayak.