If you ride in marginal conditions, then I would be very leary about getting too deep a lug. I ride exclusively in 'da UP, and still used to have over heating troubles with my 2" lug track on those mornings when the trails are frozen hard.
I am much happier now that I run a 1.5" track....still plenty of bite for the deep stuff, but fewer problems with overheating.
I would also suspect that closed track windows would NOT let as much snow in during marginal conditions....just the opposite of what was stated earlier.
Clipped every third will definitely reduce weight, and clips on every window are only really necessary if you are running extrovert drivers (but then you could NOT have any closed windows).