Yes, CG should be at 25% MAC of the wing. The tail size can then be minimized for desired stability and carry no aerodynamic loads. That's not to say the plane won't be stable with the CG behind that point, just less so and more sensitive to pitch inputs unless throws are reduced.

As for steering, it doesn't take much and throw should be minimized mechanically ( the outer most hole in the steering arm and inner most hole on the servo arm ).
As for rudder throw on a trainer, I like to set 'em up like this,

At cruise power ( about 1/3 throttle ), the roll rate due to aileron is about 90 deg/s. That is, it takes 4 seconds to roll through 360 deg. Most people might find that slow, but it's quite ideal to start, being well harmonized with elevator response. Then, since trainers have dihedral, they will roll with rudder input. Full rudder deflection should require no more than 1/2 aileron to compensate. This way, if you ever have a problem with the rudder servo going hard over ( maybe from shock from hitting the nose wheel too many times? ), you have enough lateral control to compensate. It's a safety thing...