Hi! I haven't been active here the last little while, but the job you have ahead of you is going to be very gratifying when it's done. One comment, the top and bottom exterior stripped bolt holes remind me of a broken away awning
. If you are not going to put back what was there before, just glass over it. However, if you want to mount something (such as an awning), I recommend the following.
Fiberglass in a piece of good quality 3/4" plywood on the inside, at least twice as wide and twice as tall as the external item bracket. By good quality I mean essentially void free, such as baltic birch.
Re-drill the bolt holes.
Install a t-nut on the back of the plywood for secure support.
Don't worry, we've all been there at one time or another!