I wouldn't worry about moving the firewall back any. My stock one with the firewall in the original place balanced out fine with the radio gear and battery in the location indicated on the plans. That was with a Magnum .91 4-stroke.

With the Ultimate Hog I knew I would have to move the firewall back some to shift the CG back a little and to make up for the extra weight of the 1.08 2-stroke.

Both the 1.08 and the .91 4-stroke had enough power to hover. Your Saito .72 will be plenty of motor, but you may need just a bit more power to pull out of a hover.

I used the stock aileron setup on both my hog bipes. They have worked out fine for me. I used standard servos in both. The wing is pretty thin so you may have a lot of your servo sticking out the bottom of the wing if you mount it upright.

I'll look around on my computer at home and see if I can't come up with some pictures of my mods. I knew i took some at one time but don't know if I can actually find them anytime soon.