The tank size will all depend on the snake if it will get stressed or not. I usually try to start my snakes in an adult size tank to save money. You shouldn't use bigger hides, just more of the appropriate sized hides, and clutter it with fake trees, and fake logs. You could use a larger water dish, just don't fill it up all of the way so you do not run the risk of them drowning.
As for heating, you should use two under the tank heat mats. One on the cool side set to stay between 80- 85 degrees, and one on the hot set to stay between 90- 94 degrees. However, if your ambient air temperatures fall below 75 degrees, you would need to get a heat bulb, but they need belly heat to help them digest. Also, to control the under the tank heat mats, you would need to get a thermostat, otherwise, you are risking a major burn.
Hope that helps!