I've seen many people really overdo it with expo. IMHO over 50% causes you MORE problems, because once you are past a certain point on the stick, movement accelerates.
Try this on a rudder and you'll find that you'll be unable to keep your plane running down the centerline, as you'll always be overcontrolling.
Yeah the first time I used expo I was told to use 60% on high rates, and it felt like nothing was happening, so I used some more input, and next thing I knew the plane was sideways! 50% seems to make enough of a difference. Now that I'm looking at my radio, I have -20, -15, -25 on aileron, elevator, and rudder on low rates, and -50% for all 3 on high rates, though that might change after a few more days of getting used to my plane. Just for example, my dual rates are 100%, 70%, and 60% on low rates for aileron, elevator, rudder, and 120%, 115%, and 100% on high rates. I forgot I changed some stuff around the other day.
I don't know anything about 'setting up a plane for rudder only turns'. I would just set it up as the manual states, and fly like you know how to fly. Get some altitude and start playing around. If you want to learn to use ailerons, get really high and don't use your left thumb unless you get in trouble. For left turn, bank with a little left aileron input, back to center with some up elevator, level out with some right input, etc. Play around with it and see what you like or what you feel should be changed.
Again, start out with low rates using maybe 15 to 20% expo.