Let's start with one problem, and solve it first.
The wood transom has rotted out and the fiberglass has worn away or been broken off.
Begin by opening up this area and seeing how bad it is.
Without cutting the exterior skin of the hull, chisel away
the interior fiberglass covering the rotted wood.
Once that layer has been removed, take out all the rotted wood.
Post pictures as you work, ask questions as needed to continue.