Thinking about going this weekend (July 11-12) depending on the weather. I'll probably follow the 'normal' plan take the bus to the 5th station on Saturday midday/afternoon, hike up to a hut, hang out for a few hours, and then continue to the summit to see whatever sunrise can be seen depending on clouds.

I think I'm fine gear-wise (clothes, boots, gaiters, headlamp, etc) but am curious about a few things:

1. Water. If I bring bottles can I fill them at the hut/lodge where I stay? People say the water is 'very expensive' on the mountain -- does that mean JPY 500 for half a liter or JPY 1000? I'm leaning towards carrying a couple of liters max and buying more (I try to drink 3-4 liters per day when hiking).
2. Descent. Are there any places to get water or um, 'use the restroom' on the descent?
3. Crater. Worth the hike around the crater rim to see the actual summit?
4. Phones. Is there mobile coverage at the top?
5. Any suggestions about which station to stop at / rest at a hut/lodge (one with reservations by email is a big plus) would be most welcome!
6. Any other tips or hints?

Thanks in advance.