Hi, I haven't built a Skin on frame boat, but I plan to after I finish the Guillemot I'm currently working on.
From the research I've been doing:
Ash may be a bit heavy for a frame.
Nylon stretches more than Dacron.
You are in the right range for cloth weight. I plan to use polyester (Dacron is polyester) and coat it with water based Flecto Varathane floor finish.

You should have a look through the archives at:
http://rtpnet.org/robroy/baidarka/