Miscellaneous Questions about Lindblad/National Geographic Antarctica trip

I am getting ready to go to Antarctica on the National Geographic Explorer on January 7. I am pretty much prepared and have read a ton of trip reports on various boards but I have some miscellaneous questions that I have not seen addressed. I usually travel independently and have never been on a cruise, tour or expedition so I'd like to know what to expect. It would be great if someone who took Lindblad can respond, but experiences on other boats would be appreciated as well. Thanks is advance for any help!

1) What is the water situation on the boat? My understanding is that the cost is included in the trip. Do they leave a set amounts of water bottles in my cabin each day or do I grab my own from some kind of cafe? Both me and my companion always drink A LOT of water (probably 4 liters each a day) and want to make sure we will be getting enough to drink.

2) What sites are included in the Santiago City tour that is part of our trip? Are Cerro San Cristobal or Parque San Luca included? We are arriving one day earlier than everyone else and might explore a bit on our own but don't want to replicate sites?

2) How does the shift system work. There are 148 travelers on the boat and I read that only 100 people are allowed at once. Do we all see the same sites? How is it determined who is on the first shift or the second? Is there one you prefer? I would think the first is best so you don't have to wait around.

4) Where is the best place to buy souvenirs? Port Lockroy (assuming we visit), boat shop or is Ushuaia after we disembark? I don't want to rush to buy stuff in the beginning but a lot of people have requested souvenirs from us and don't want to miss my opportunity. Do we have time to buy souvenirs in Ushuaia after we disembark? My understanding is that we would be allowed to explore before our flight back to Santiago but I wanted to be sure.