I would do it in stages. Put in a couple of of layers of cloth, get rid of the air bubbles, let it harden, then a couple more, repeating untill all 3/8" is filled. When all is done, apply the last layer of roving on the inside.
I hesitate to put a layer on the outside because fairing it will be a real pain and you'll probably sand it all away anyway. That's why I suggested using collodial silca as a fairing. You can usea a lower density West fairing compound, but the silca is really strng stuff and this is an important repair.
To put the repair in perspective, it's a small hole and not in a load bearing area, so ther really isn't a need to cover the outside with cloth. After you fill with all the layers of roving (NOT mat) and the final layer inside, the repair will be as strong as the area around it. MAYBE if you pounded a hammer on the exact hole, MAYBE it would give, but I doubt it. There may be some disagreement on this, but I would feel confident with this repair on my boat.
All things considered, this is a simple repair and can be completed in a couple of days (most of the time is spent waiting for the epoxy to cure). A note of caution - don't cheap-out and use fibreglass resin. Use epoxy.
Sabre 38 "Victoria"