Welcome to the forum!

Good idea to use the .020. and more wing area.Mine had the .010 and I built it too heavy for it to fly very well. The weight needs to be to 5 ozs. Mine was 8oz and that was too heavy.
You only need two channels. I think I would go with ailerons and elevator. You need to have less dihedral with ailerons.I had rudder and elevator and it was very sensitive to the amount of throw. I think I had 3/8 inch total throw on rudder and about the same on elevator. If you use landing gear mount the wire on the front of the plane only,as a tail dragger.

I built a 150% size version (30 inch span)with a .049 Black Widow and this combination is fantastic! I fly it with 2ch, rudder and elevator. Lots of fun.