The METAR is only going to give you touchdown RVR. The Federal Meteorological Handbook Number 1 (the observers guide) says the RVR sensor used for the METAR should be within 500 feet of the runway centerline and within 1000 feet of the runway threshold. They can report up to 4 different runways.
To takeoff in lower than standard TO minimums the airline must be approved for lower than standard TO minimums in their OpSpecs and the crew must have been trained to that lower minimum. You can only operate to higher of what your OpSpecs allow or what the chart says.
In your CLT example the chart says two transmissometers are required and all are controlling to takeoff at RVR 500. In addition the runway centerline lights and the high intensity runway lights must be operational. If either of the lighting systems is inop you are limited to RVR 1000 even though you may be approved for RVR 500 takeoffs. And you would still need 2 operating transmissometers and all are controlling.