I own two Serato DJ Intro controllers, do I have to buy two Serato DJ licenses?

No, when you purchase one Serato DJ license, it will activate Serato DJ for that computer.

This means that you will be able to connect any of the supported Serato DJ controllers to your computer and the software will remain activated, regardless of the controller you have connected.

You can deactivate unwanted computers from your account through the MY SETUP screen inside the software.