Wing dihedral is used to make the plane more roll stable, which is very important if the plane does not have ailerons. High wing dihedral tends to make trainers fly with wings that level themselves. A plane with ailerons does not need the stability of dihedral because the pilot is able to use the ailerons to keep the wings level. Soo ... installing ailerons means you can reduce the dihedral. If you keep in the dihedral, the effectiveness of the ailerons will probably be reduced. If you are learning to fly, use the standard wing with dihedral to learn on, and then build a new wing with no dihedral to put the ailerons in and use that as a second plane. I did that many years ago. I think most high wing planes with ailerons have no, or very little dihedral.

I remember seeing a Senior fly a long time ago, I seem to remember it was very slow and heavy. Addding weight to it may make it even worse. You will probably be better off to buy a 4 channel plane after you learn on the 3 channel Senior. Adding ailerons are easy if you have built a wing or two for 4 channel plane. If you have to ask how to do it, it is not so easy to explain.

I have never used solartex, don't know anything about it.