If the snake is looking dull then yes, it's probably a shed coming.
It isn't always necessary to actively increase the humidity IMO, it depends what your home is like. My house is fairly humid anyway and two of my snakes always shed perfectly without me doing a thing. I spray the third snake but she requires higher humidity anyway.
Definetly keep an eye on the humidity, though, especially as it sounds like this may be your first shedding experience.
Yup. I live in Virginia. As a hatchling Raydin always got it's viv sprayed and I sprayed the snake itself a little bit with very light misty water. However I tried going a couple sheds without this just to see if the snake needed it or not and the snake was fine. Ever since then every shed has been a perfect one piece shed.
No problems. If you live in an area where the air is not as dry and you have natural humidity in the air most days of the year your snake will be fine and you need not worry about humidity.
Plus depending on your substrate and water combo you will get some more natural humidity in there without even having to do anything else. Alot of people don't realize that as well.
Virginia = humid
Texas = Not so humid almost dry... in the southwest it may be a good idea to add a bit of humidity.
They're cheap, and even if you live in a humid climate I don't see how putting one in there could be harmful.