Hatchling or yearling will be fine..get whatever you like. They are not like a puppy, if they are nippy they will probably always be nippy. Raising them and lots of handleing will not always calm them.
I would stay away from the wooden hide, it will get soiled easily and be harder to clean. Lean towards plastic. I stick with a hide until the snake stops getting under it or shows signs of stress. Each animal is different.
Either live or FT is ok. Some BPs are reluctant to take FT but other take right to it. FT is cheaper but S/H is a killer. Weigh your local options, you may can find a rodent breeder near by to get rats from.
Humidity can be created by using 2 UTHs. A regular sized one for one side and a smaller one on the other, keep the water bowl on top of the small one. Also cover 3 sides of the tank with corkboard (from Lowes) Avoiding heat lamps will help with humidity too.
Good luck with your new snake.