Here's a fascinating article from Advantage Petcare. It's called How to crate train your dog, fast.
There are some really thought-provoking insights here. This one about crate size is particularly interesting:
Size is an important consideration when looking for a crate. The crate should be big enough for your dog to stand up in when fully grown. If you’re buying a crate for a puppy, take into consideration its estimated adult size and weight.
Measure your dog’s length and height and know its current weight and anticipated full-grown weight. Knowing such numbers will help you select ...