Hi Anotny-
Licensing for W3 Total Cache Pro is on a “per-install” basis. That means if you’re using WordPress Multisite for your websites, you’ll only need one license for the network. If your sites are separate installations, you’ll need a license for each site. If you’re interested in Pro for multiple sites, contact our sales team directly from your WordPress Dashboard by navigating to Performance > Support > Sales Questions and we’ll be happy to come up with a solution that fits your needs.