Cubase License: just deactivate the license on the old computer in the Steinberg Activation Manager.
Then install the Steinberg Download Manager on the new system, install Cubase and activate the license again in the Activation Manager.
That should so it. I wouldn’t hurt to check if you have third party plugins installed on your old system, sometimes those need to be deactivated, too (best example e.g. iLok with Machine Authorization. Very important to deactivate the old system).
you might want to check out this for backing up all Cubase preferences and settings files and restoring them on your new system