Just for what it's worth, making your own balsa ply is unlikely to give you straighter wood than you now have. My first build getting back into the hobby after a 40 year absense required laminating 1/16 ply onto 3 /32" balsa for the sides from firewall back behind the wings. Iused tighbond for the glue. I glued up the pieces then seperating with wax paper, I clamped them using some 4quarter x 4 stock and let them dry for a couple days. When I pulled them out of the stack, Ihad two badly warped pieces. Idecided to go with them and I had to use a couple 8" C clamps with verticlal boards to try to straighten the wood to the two main formers. What the end result was that I still had warped sides, not length wise, but from top to bottom. This was really appearant when I tried to cover it. Iwas trying to cover the inside of a pipe sawed in half. The big clamps let me get a good glue joint on the formers, but inbetween the warp was still there. The fuselage ended up like a bannana. After all this, the plane still flew quite well until I dumb thumbed it into the ground and killed it three years later.

Don't sweat the warped ply sides. When you get everything together, it will be straight as long as you follow directions well.

You probably don't want to know how warped the wood was that your house was built with. It all works out if the build is good.

Don