I use pothos in all my snakes' cages.
1) I just pulled the plants out of the nursery pots and washed them off, roots and all in tap water. Then just planted them in my own terra cotta pots with organic potting soil. Worked fine.
2) All i use is terra cotta pots with organic potting soil. The pot has its own drain hole in the bottom. Just dont use too big of pot or the plant will probably get root rot. I learned that the hard way. Better off being a little root bound with Pothos.
3) The snake wont pee on it. I would be more concerned about the snake flattening the plant as all of my snakes have climbed on the plants or dug in the pot and uprooted them.
If you keep pothos, they dont need a lot of light and my advice for watering is wait until the top inch or so of soil is dry or the leaves start to not look so perky. Being in a viv, they dont need that much water especially if you are using less light like LEDs.