There is no limit for a person to have VK. You can have one, two, or any number of VK with you. You can use all VKs for the “boost method” as well.
Some Reiki practitioners have 10-15 VKs. They use all VKs to give energies to their clients. They just simply request VK for the energy and VK follow their request. In that way, they get enough time to talk with their clients. Must check: Innovative Ways to Boost Your Manifestation With Multiple VKs.