Selfhosted

So I'm quite new to the self hosting world, and not the most tech savvy, but I'm looking for a way to expand and increase the reliability of my file storage. I used to just use cloud storage but got concerned about privacy and environmental impact and whittled down all of my data to about 200GB including all my music, photos, movies, backup files, etc. I have a laptop, phone, and mp3 player and currently use synching to sync all of my files across all three devices. This works great, I love how seamless, cheap, and automatic everything is. But I want to expand my storage abilities and include a backup that isn't with me / in my apartment. I was thinking of getting a couple raspberry pis with m.2 ssds, one to leave at my sisters house (small and unobtrusive little plastic box connected to power and her wifi) and then one at my apartment to act as another node, freeing up space on my phone so that all my files are in at least 3 different devices (3:2:1 rule?). this feels like an fairly easy project to set up, but I have a feeling there is probably a better way to go about what I'm trying to achieve.

Edit: Thanks for the advice y'all! I ended up deciding to keep things simple and get a few ssds to do simple weekly local backups on with Vorta. For offsite, I'll just rotate drives, leaving one at a friends house.