RE: what to use for main spars?
For those who want to know more about the structural properties of wood read [link=http://www.fpl.fs.fed.us/documnts/pdf2001/green01d.pdf]THIS![/link]
For those who want to maximize the strength to weight ratio of their spars start [link=http://en.wikipedia.org/wiki/Second_moment_of_area]HERE![/link]