you might want to call bob holman and ask him about those extra ribs. i've looked at the plans and the confusing area to me is the retract area, i have the typhoon plans and they kind of lay it
all out for you on the retracts, they dont on the corsair. lightening holes on metal are supposed to ( circular holes) increase strenth, i dont know about balsa. taylors are supposed to build lighter, you may not need them.

happy bird day