Circumference would be about 94" -- so a dozen to 15 would be plenty. I would calculate how many I wanted and even spacing for them (one per brick, two per brick, whatever) and then drill maybe half of them, light a fire and see how it burns.

On the other hand, you can't really have too many, so you can do them all at once if you want.

I'd get a small piece of plywood so you can lay the drill on it's side and just push, instead of having to hold it up.