I'm not sure what to say about the quantity of glue. I've never attempted such a repair myself. I have read about guys making custom ducting for car turbo systems using silicone seal and fiberglass, and that is where I got the idea for your repair. With regards to the fiberglass cloth, the 3/4 Oz cloth is pretty specialized for its light weight. The RC guys use it on their airplanes because it is so light and strong. You might find it at a hobby shop, but not at your typical hardware store.
I would make a much larger patch with the fiberglass and tape it down to a large ZipLoc bag. Then, saturate the cloth with the glue to wet-out the cloth. Remove as much of the glue as you can once the cloth is saturated. Apply a thin coat of glue to the area of the hole about the size of your intended patch. Use a razor blade to cut out the size patch you want, then transfer the patch with the plastic bag as a stiffener and position the patch over the hole. Tease the patch off the plastic with a tooth pick and allow it to dry. Alternatively, you can leave the plastic in place until the glue dries, so long as it does not cause the patch to lift away from the surround (you might want to test this first, to make sure the plastic will pull away from the glue after it dries).