The flow required is not based on the valve but is dictated by the diameter of the media tank and the media contained. The larger the diameter and\or the heavier the media, the higher the flow rate required to properly expand and clean the media bed.
The valve needs to support the tank size required which the 7000 will support tanks from 8" - 24" diameter. Your pump and plumbing need to supply the DLFC required to adequately backwash the media.
For a water softener, the media (resin) is not heavy and so does not require a high flow rate for backwashing. The DLFC for a 10" diameter tank (1.5 cu/ft) is typically 2.4 GPM whereas a 12" tank (2 cuft) will need about 3 GPM. Unless your water requirements are unusually high or your water is extremely hard, most residential requirements will be satisfied with a 1.5 or 2 cuft softener.
Is regeneration scheduled at night even if it is metered?
Metering will only tell the controller when a set volume of water has flowed through the softener. Once a specific volume has been reached, regeneration will be triggered but regeneration will likely not occur immediately.
With a single tank softener, soft water will not be delivered while regeneration is occuring so regeneration is typically delayed to a time when soft water is unlikely to be needed. In a home, soft water is not required continuously as most occupants sleep at the same time. Regeneration is typically set to occur when everyone is sleeping.