You have about 1/2 inch of balsa in the wing and tail section to hold the 3/16 Robart hinge points. This is plenty for I have 49 flights on my Patty with this setup and have had no problems.

I used two Hitec 5625 digital servos on the rudder with a "Y" harness and never had a centering problem. Just take your time setting up the system.

I believe the supplied control horns are fine.

Last but not least, I don't believe you need two battery packs and switches for the receiver and servos. Just check the battery voltage before you fly and use a good heavy duty switch. But if two battery packs make you feel safer in the air by all means go for it!