Get you a straight, clean, osage stave forget the boards the heat (straighting,or reflexing) the backing and everything else your hereing.
Just make a 64,66 inch simple bow. You can get a bow in the 40,50 # range easy. If you've broke as many bows as you say you won't have a problem makeing a simple osage bow. My oldest son made a osage bow a 12 years old. I still have it and it still shootable. And he did it with out the internet.
Don't sweat it if you really have the desire you'll make that bow. And beleive me once you do there's nothing like shooting ,hunting with your own bow. Take a deer or turkey or what ever you hunt. You'lljouin a club that not manypeople belong to.
You'd almost have no exsperance at bows at all to screw up a straight,clean osage stave.
I use the KISS METHOD on just about everything.
KEEP IT SIMPLE STUPIT.