Well I would set everything thing up. substrate, hides , water bowl filled with water ,any foliage , everything but the snake. once you have your UTH running leave it on overnight. then in the morning, check the temp of everything(I use a temp gun). Your heat gradiance should be 85-90 on hot side and 75-80 on cool end and a humidity around 60%. If the tank doesn't reach those requirements then you need to get a basking lamp. The wattage you will have to buy and test to see what fits your tanks needs. But if your tan k is running too hot just with the UTH then simply turn down the thermostat.
VERY IMPORTANT!!!!! Temp gun everywhere... Temp guns cost around 15$ on amazon. use it under your hides, on your substrate, the water, the plants, any decorations, everything. Also if your using a UTH, I like to but the terrarium liners under my substrate. This allows the snake to burrow and not lay directly on the hot glass under neath your substrate. They are maybe 5$ a roll.