One more thing to add is that if you just put everything in, give it a couple of days before you freak out about humidity. There's a certain amount of moisture in the substrate when it's in the bag, and it will take awhile to equalize and settle in where it's going to settle. If your humidity over all is too high, increase the ventilation in the cage (exposing more screen top, drilling more air holes). If it's too low, decrease the ventilation (covering screen tops and air holes, etc)
The other thing about humidity is that the % numbers you hear about are *relative* humidity, meaning that it's a percentage of how much moisture the air can hold before it condenses, and that varies with temperature. So the humidity might well be different in different parts of the enclosure where the temperature is different, and that's OK.

You can get an electronic thermometer/hygrometer really cheap and easy, they're just the little digital ones people use in the house. Some come with a wireless (or wired) sensor that you stick outside, and it tells you the temperature inside the house and outside. Get one of those and it will tell you the temperature in two different locations in your enclosure. Acurite is a popular brand, but not the only one.

Hides can be boxes, upside down bowls, tubes, all sorts of things, not just what they have at the store. Flower pot dishes with an entrance cut out are popular.

I know it seems daunting to set up, but once it's all set up, a ball python is one of the easiest pets to care for that there is. Read through the various set-up threads, even the ones about different kinds of enclosures than yours. They'll still help you figure out heating, thermostats, thermometers, hides, etc.