I agree with Minnflyer. I wouldnt go completely flat until you have a few more flights under your belt. if you wanted to make it a bit more sporty, than you might consider taking out about 6 inches off each wing tip as well as maybe taking about half the dihedral.This will increase your roll rate, but still leave some stability. (The dihedral is what gives it stability in flight) When you get to the point of being completely bored with the plane, you might try and change the plane to a tail wheel. The LT-40 makes a good tail wheel trainer. As far as wing shape is concerned. The flat bottom airfoil creates more lift, but does not perform well when inverted. by making the wing symetrical. (curved on both sides, the plane will fly inverted as easy as it will upright. Symetrical winged planes are more difficult to fly. Once again.. I wouldnt recomend going to a symetrical airfoil till you have another gallon or so of fuel under your belt. I always recommend to my students to be absolutely bored and to be able to do EVERYTHING the plane is cabable of before moving on to their next plane. Good luck and smooth landings!

FW