Its easy to get the wings on an Avistar a little crooked when you put on the rubber bands. What I do is find the center of the cross section(side to side) of the fusalage right in front of the vertical stab and put a small mark with a pencil or ink pen. Then measure from this point to each wing tip or tip of the aileron and postion the wing so the measurement is equal on both sides. Do the same for the elevator, find the center of the top of the fuse right in front of the wing Le and mark it, then measure to each tip of the elevator. Of course if you've already glued the elevator, you may just want to live with it if its less than 1/4" off.
After I get the wing squared up, I make marks with a sharpie on the center of the front and back edge of the wing as well as the fusalage, from then on all I have to do is line up the marks when installing the rubber bands.

Not sure what you meant about the Kadet, but it is no step up from the Avistar, the Avistar will out fly it any day with equal engines. However , A four star, Kougar, or a Somethin extra would be a good next step.