Don't use Maple or Birch unless you plan on a 3 year boat. WRC is fine for planking stock, but you can do much better, and for less money. Why use Red Oak when you can use White Oak?
I don't mean to be............ Curt....... but think outside the box. You must be looking at local comercial contractor type lumberyards...... Ask around. You can find the proper stuff, at reasonable prices up there..... You're in lumber heaven!
Why wouldn't you be able to join your Mahogany transom? If you can't do it by hand, Im betting dollars to doughnuts that there's a cabinet maker within 10 miles of you that would gladly run a couple of piecesof lumber over his jointer in exchange for a few bucks, or even a ride on your boat when it's done..... (We tend to be pretty nice guys....)
And yes...... Western Red Cedar (WRC) is toxic to many people.
Never trust a man with a clean workshop.