I am doing much the same with my Mk II, and although I am not there yet, I intend to use Danboline for inside the bilges as recommended above.
I would say however that gelcoat or glassfibre resin (polyester resin) would not be my choice as this type of resin works by cross-linking the polymer chains which works fine with fresh resin, but after a few years the hull resin will no longer cross-link and you will simply be painting on top the existing construction. Epoxy however is a real adhesive (as in Araldite) and will make a strong and tough repair.
I would recommend that before you start the repair, go over the area with a de-waxer and de-greasant (I have a tin of the stuff by Blakes which seems to do the trick) keep turning the cloth to ensure you are lifting contaminants off, not just rearranging the grime of ages over the task area. Then abrade the surface using something like 60 or 80 grit abrasive paper and complete the repair using epoxy resin and woven glass cloth (not chopped strand mat which has an adhesive that will not dissolve in epoxy). Finish by washing the amine blush away with water and a Scotchbrite after curing and after a light rubbing with finer abrasive paper especially at the edges of the cloth, give it the Danboline treatment.
As for the external paint system I have used International Paint products successfully before, I would suggest you use Toplac, do not use the two-part Perfection on top of anything you are not sure of. I am using Brightside, but distressingly, IP have just withdrawn that range from sale; fortunately I have bought quite a lot (about £200 worth)