This was my third butt, fourth smoke (first was ribs). My Maverick ET-732 was giving me fits varied between LLL's and 50-60* readings, which couldn't have been right. The thermo on the door of the smoker was consistently reading between 200 - 250*. I know that thermo is off, but can't remember by how far. I've relied heavily on my Maverick, so when it started giving me wierd readings I was kind of driving with very dim headlights. I think I was able to keep it down at 225 - 230, but of course I can't be sure. The Maverick would periodically give readings in this range, and the thermo on the door at least told me that the really low readings on the Mav were BS. So, the answer to your first question is around 225 - 230, although I can't be for certain.
I foiled it around 180* IT, but left the smoker temp alone, since I thought I had decent temp established. Incedentally, it appeared that the food probe on the Mav was working okay. I bought a regular stick type meat thermometer at the local grocery store yesterday afternoon, just to test it, and got readings consistant with the Mav. I've since ordered a replacement smoker temp probe for the Mav. I went out at 199* to take the foil off, and the butt literally fell apart when I tried to pick it up out of the foil. At that point, I re-foiled it, and shoved it in a cooler packed with towels for about 1 1/2 hours. I pulled like a dream, and was very moist at that point.
I didn't put a finishing sauce on it, and that may be the reason it dried out.