Do I install the official LTX Desktop first and add this as a plugin?

No. The installer is the desktop app. It uses the same installation identity as LTX Desktop so it replaces that app on Windows rather than sitting beside it as a second editor.

You do not compile the app to use it. Customer access covers installers, installation guides and license notices. The private development source repository and its history are not included. Existing upstream open-source rights and prior license grants remain applicable.