RE: Foam core wing repair
Layout a square pattern around the damaged area about 1/2" beyond the damaged foam, cut the balsa on your layout, and carefully remove the balsa from the foam core. Now tailor cut a virgin piece 1/8" thick balsa that fits inside your cutout, use Gorilla glue and brush into the damaged area and the surrounding foam that you removed the balsa from. Lightly spray the area with water and place the 1/8" thick balsa skin over the area, immediately cover with a generous piece of Handy Wrap, place 6 or 8 model magazines on each side of your wing while laying horizontal on a flat surface and gently place anything weighing around 25 pounds directly over the repair area. Allow full cure, remove weight, magazines, and Handy Wrap, spline sand area and recover.
There is another effective way to do this utilizing a vacuum bag and caul plate but you stated that this was your first repair and I am thinking that you may not possess a vacuum pump and all the rest of the garbage needed to perform this simple repair by the means I already explained. Best of luck to you.