For holes, I taper the repair to maximize the surface area for the epoxy bond.
I prefer to use about 4 layers of 4 ounce fiber glass cloth to build up the patch. I build my patches by layering the fiberglass starting with the largest piece on wax paper. then add increasingly smaller pieces of cloth in an attempt to match the sanded tapered hole. I then saturate the "patch" with good quality epoxy and flip the patch and apply the resulting semi solid result to the hole.
Last wait a few days before trying to apply the gel coat, as the curing epoxy can make a mess on the curing epoxy, Thus far I have yet to have a boat come back after a repair.
The point being is a decent repair can be made and it will hold.

I hope this helps,
John VB