I have never done this trail in the winter, but when I went in April this past year shortly after early ice-out was announced, I believe I was the only one on the whole trail for three days (bliss!). Based on how booked up the trail typically is, I was surprised. If memory serves, I didn't see too much evidence of winter camping near the lookout point, aside from maybe the remnants of one or two fires in the vicinity.  I assume that it does not get much winter camping usage in that spot. There's a great open area to setup camp a very short distance away from the actual lookout. I would think the trail can be travelled in either direction without issue, but again I have only done this (in different directions) in non-winter months. As for water supply, the Madawaska west of the lookout would be a safe bet as it's quick flowing/cascading here. I'm not confident of any other areas as I seem to recall other creeks and streams to be narrow and slow moving. Maybe someone else with more experience can chime in?
Hope this helps, for what it's worth...
Cheers,
Rich