Wow! It's a land of opportunity!
I wish you well. Reach out if you want any ideas. There's a lot of good historic information here, and a good group to ask detailed questions. At the state of your remodel, I'd get rid of the screws that go through the shell, and put some interior strips in place, adhered to the fiberglass. Grind the inside to provide a rough bonding surface and use a fiberglass compatible adhesive. Use the screw holes to hold in place until hard, then remove the screws and fill the holes from the outside. Our experience is wherever there are screws through the shell, they will vibrate and become loose or allow water through to rot the wood. My two cents, but it's what we did and we LOVE ours now that it's complete.
Randy and Ranae