As others have said, you don’t have to be concerned about anything if you keep good backups. Disk storage at this time is very cheap compared to what it used to be, you could probably find a 5200 RPM 5 TB disk for ~100 dollars USD, or even better, two 2 TB disks which you could configure with software RAID.
It does look like obsidian to me. People like this or logseq a lot for their note taking. If you want a foss alternative, you can look at Joplin, though I can’t recall if it has a graphing feature like this out of the box.