I think most have gone away from the gybing boards by fairing in the daggerboard trunks.

You've pretty much got the repair down.

Don't worry about the gelcoat over epoxy - it's not really an issue in small patches like that. Just rough sand (150 grit) the epoxy patches before gelcoating so it can get a decent mechanical grip (same goes for the rest of the recoat). Some of that gelcoat over epoxy is blown out of proportion based on the fact that there will not be a chemical bond between gelcoat and epoxy (which is true)...but you're not going to get a chemical bond between cured 5 year old gelcoat and new gelcoat either.