Polyester resins are most likely the resin used in the original boat build. When bonding new polyester to old, the bond is primarily a mechanical bond, not quite as strong a joint as the original chemically bonded original laminants.
Epoxy creates a chemical bond even when bonding new to old (or secondary bond), and will be equally as strong as original laminants (primary bond). Epoxy will secondary bond well to polyester, but the opposite isn't usually true.
Epoxy is much more viscous (resists pouring) than polyester.
As for wood choice: A single layer of glass laminated to the wood with resin will not add much, if any strenght. It will help the wood resist moisture, and make it more durable. Therefore, the strength of the stringer or floor or whatever you are building will come from the wood selected. Hardwood, or several layers of marine plywood are the typical choices for stringers and other structural members. Obviously marine ply is the best chioce for the floors. If the wood components are to be laminated, one could argue that Marine grade might be overkill. Exterior grade plus the fiberglass will probably give more than enough years of service.
No doubt you have noticed the soft wood (the back seat for instance) the manufacturer selected to save money, and it lasted a long time.