Do I have to buy a Serato DJ Pro license and activate it?

It is not necessary.
Connecting the DDJ-REV7 activates the Serato DJ Pro so that you can use the software when the unit is connected.

To use the Serato DJ Pro even when the DDJ-REV7 is not connected, you may need a separate license.
For details, visit the Serato website [[serato.com]] (https://serato.com/dj/pro/buy-dj-pro ”https://serato.com/dj/pro/buy-dj-pro”)