Pi NAS for multi-location backups - sh.itjust.works

Over the past few months I’ve been thinking about what would be the best way to help me and my parents improve privacy and data storage. With all the posts with cluster PC’s recently, I’m wondering if the best option is to make a couple of NAS’s with Raspberry Pi’s with RAID, keep one at my place and another at my parents’ house, and syncing their data with 2 private folders: one for myself and one for my parents. But that opens up a few more questions. How to sync the data to match? Syncthing? Kubernetes? Should I make the Pi’s expandable so other services can be added later, or plan to hook up a separate Pi to handle that? What else could I be missing?