Hi!
You can use whatever dimension you like ...within reason ofcourse. Just use whatever servo arm you like ...preferable as short as possible at the servo and make the rear rudder or elevator horns as large you like ...short at the servo and large horn at the rear is what one should always strive for to have a tight set-up.
I always use wires whenever I can...in my 375km/h pylonracers as well as in my sport airplanes and scaleairplanes. Wires could be bought in fishing stores.
See pictures of my Great Planes GEE BEE R-2 ARF airplane.
Regards!
Jan K
Sweden