Dremel 663DR Core Glass Drilling Bit, .25 in Dia

I've started making bird feeders out of old glass plates and bowls. Picked this bit up at a local big box building supply store and found it to be exactly what I needed to cut through many types of glass. It has a hard time through anything thicker than 1/4" but I have managed (with patience) to get it to cut up to 1/2". I have cut nearly 20 holes with this bit so far. I have three questions. 1) Is it better to use the cutting oil or a constant supply of water to cool the bit? 2) How fast should I be running my Dremel tool for the best and smoothest cut? I start out about mid level RPM and increase the speed the further I cut into the glass? 3) How many cuts can I expect before needing to replace the bit? Thanks!