For Gillmen, well, since I did see Jupiter Ascending, I'm going to allow for the purchase of emergency water filled suits, colloquially called "Dunk Tanks", 1 for 10 gp.
Also, you have your water tank to sleep in. It's not incredibly hard in my mind to make a container full of water, so go for it. Additionally, food and water on your ship won't be something you need to keep track of-assume really good water recyclers and crates upon crates of soy, which, while unappetizing, will at least keep you going. Resupply on world is what will be the problem.
And speaking of money-same system, just replace "pieces" with "credits" (So, copper credits, silver credits, gold credits, and platinum credits).