Hi BG,

It looks like your request drew no response. so I'll offer my humble opinion. Since this a small foamie, the hinge material best suited to the job is clear packaging tape. Put the tape on the top side of the wing centered on the hinge point. 20% of the chord is probably more than you need unless you are looking for extreme flight capabilities. Don't bother with individual servos for each wing, the weight will be a big disadvantage and you don't need the power for a small and light foamie.