Looking forward to seeing how you progress with your large autogyro, I have started building a large gyro to be powered using a Laser 150 vee twin. Unfortunatly due to other projects and financial reasons (large powerful servos needed) so this has been shelved for the time being. My only advice at this moment in time is to keep it as light as you possibly can for good flight peformance...every gramme saved in weight is worth it..Im not sure how long your blades are? the largest I have built to date have been 100" span and these are constructed of bass wood and balsa, they use a flat bottomed clarke y aerofiol and seem to work well.
Im looking forward to how your build unfolds.

Regards Rich