As far as the tapered leading edge goes, you need to compute the MAC. (That's stands for Mean Aerodynamic Cord) this is the average cord taking into account the length at the root, the length at the tip and the sweep. I don't have the formula at hand but you can go to http://www.geistware.com/rcmodeling/cg_calc.htm#cg
and fill in the info and it will do it for you. When it wants what percentage of MAC, you want to start with 25%. OR if it were me I'd just balance it on the wing spar!