Ok, first off let me commend you on doing some research before you purchase! no on to your questions.
1. Tub size. I would go with a 15 quart tub, if its the snake in the picture. Not sure of the sizes off the top of my head.
2. You all ready have that one answered.
3. You can get the melamine at Home Depot or Lowes.
4. Not real familiar with Zilla thermostat. Johnsons and Ranco's are a decent mid priced thermostat and Hydrofarm has a lower end thermostat that a lot of people on here use as well as myself. Thought I would try it out and so far so good. Can find it on ebay or Amazon.
hope any of this helps,
Dave