Is the area around the hole soft? Is the glass cracked and has limited strength? If it is, you still need to grind back to a point where it's solid.
I pretty much agree with everything that's been suggested, and when I patched the hole in my hull I thought I was going to have to back it, but in the end I didn't. The actual hole was more of a 1/2" by 3" gash, but was still soft around the edges. I cut away as much of the loose glass as possible, and ground/feathered out a good two inches surrounding it. I then filled it in stages. First, instead of making the hole bigger and installing a backer, I forced a thick fold of wet glass into the gash. Then I ground down the exterior of the fold smooth, followed by layers of glass and cloth. Then you have to grind all of this down again into a shallow dish that's below the surface of your hull. If you don't, when you shoot your build up of Gelcoat, you'll end up with a wart on the hull. Just take a flat stick and lay over the ground out area to gauge if your repair is too proud...it's sounds like you may already know to do this... One other thing I did was taped around the hole to prevent excess glass getting on the hull and causing me more work.
My repair feels pretty solid. Is it as solid as if I were able to reinforce it with a backer? Proababy not. My situation was a also a little bit different as the hole was in the side and not the bottom.
As far as your other divots. You're going to be surprised as to what you can do with Gelcoat. If they're really deep you can mix some finely chopped glass into some thick gelcoat and fill the divot. If you pour some uncatalysed gelcoat out into a small container, it'll flash off and thicken up. Add your fillers, hit it w/ the catalyst and apply. Seal it with PVA, lightly sand out the area, then after it's set just shoot over it with your finish coat.
You're going to do fine!
Hell, once you get started you might decide just to sand and shoot the entire hull