@selje :-) I would have trouble with file management when to move what, because duplicate would not work spacewise, and I assume technically impossible to share a home folder partition. Furthermore, the 8 GB RAM works but is at the lower end for photo editing, esp if later get a more pixelhungry camera. But it's definitely worth to keep in mind for ideas for how I can use my macMini later on. Thanks for your comments!

@hehemrin
That's where rsync comes in. It is unparalleled at file transfer. I have never seen an app that comes close to the features it has. All from the command line. It even supports ssh. It is available on all unix based OSes which includes Macs. Even for just moving files locally its features are mind boggling. You may already have used it, but if not I would highly recommend it. It even has a test option so you can build a command and test without worry.

@selje No, I haven't used it itself. But seems as a tool I should learn how it worls. I have used it as engine in eg Timeshift backup. BFor file backup, I'm thinking of evaluating Borg backup, both on external drive and eventually also eventually for cloud backup (encrypted). Another interesting tool is Syncthing I also may try, to sync files between devices via local network.