I wrote an article on my blog on how to move photos from google photos to Synology, if you're the kind of guy that wants to host things on a NAS: https://michelenasti.com/from-google-photos-to-synology-phot...
There's also a way to overcome the 500 photos limit (using google backup options).
Nice write up. I’m currently in the process of moving all my photos into my new Synology NAS. I can see that you prefer the terminal, but the downloading could be performed via the download station and the copying of the files via the file manager/explorer. This way the whole procedure would be more user friendly to novice users ;-)