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Twelve or so wireless cameras will not work, they will over load the wireless network. Run the network load numbers
Also for a security system wireless cameras are very unreliable. It is relatively easy to jam a wireless network.
If you need to run power to the cameras you can run POE ethernet.
Please read the
cliff notes and other items in the
wiki. The wiki is in the blue bar at the top of the page.
Read,study,plan before spending money