Centres vary in size - both physically and in terms of the number of CBP Officers who work there. The number of interview slots will therefore vary per location.

The centres only load availability for a few months in advance - perhaps anything up to three months ahead - so what you're seeing at CLT is a relatively small centre with lots of people trying to get in. At some point, appointments further into the future will be loaded and you might get one of them.

As to things like the documents you'll need - actually, that's dependant on your nationality. The acceptance document you got should detail what you need to take, but if not the one you'll receive which confirms your appointment certainly will.