Maybe around 25 or so on the first one. I had some dark juice on the second coil though and I'd say about 15 ml.
Yeah it should last longer. Look at the color of the juice in that picture I posted of the nintendo controller mod, it doesn't get much darker than that and that's 80% VG. It's in an atlantis in the pic but I use that in my subtanks as well.
As far as the popping some pop is normal but if it is spitting juice in your mouth then you should turn the wattage up a touch. Spitting is indicative of it not cooking the juice as fast as you are sucking it in.