Also, how does the clock speed work? Everything is 2133MHz by default, and I need to enable the higher clock by selecting OC in BIOS? So is the rating on the chip its maximum, or its rated maximum? Like, can I try to overclock a 3000MHz to 3200MHz?
The rating on the RAM is the maximum speed they have been tested to run at by the manufacturer. You are free to run them slower.
The CPUs Intel memory controller will be overclocked from 2133mhz to the RAM speed, so although the ram could do it, your IMC needs to also be able to run at that speed.
I find running 3000Mhz with a CPU OC do-able. More RAM speed combined with a CPU OC can make it more difficult to run stable.
XMP isn't guaranteed due to the reliance on the CPU IMC to co operate, so you should be willing to play with the VCCIO/VCCSA voltages if need be.
After 3000Mhz CL14, there is little to be gained.
You are more likely to run a 3200Mhz CL15 kit at 3000Mhz CL14, than a 3000Mhz CL15 kit at CL14.
Good modules should be a problem in either case.