The extra storage might be cheaper to come by than h265 hardware (or the cpu grunt to live transcode on the cpu). Depends how much you want to hoard I guess.
Yes you need at least 2 hard drives. You can put video you don’t care about on a single drive, but backups etc should be on a redundant disk array (e.g. btrfs, zfs, other options). And an offsite backup while you are at it.
I have 8gb ram with immich, jellyfin, home assistant, prometheus, grafana and a few other things running, but it is constantly butting up against the ram limit. If you want to add nextcloud etc to the mix then you’ll definitely need more. As it is I had to turn off some services I used to run and I’m looking at upgrading the ram.
I use debian, it’s fine.
Btrfs used to be easier to install because it is part of the kernel while zfs required shenanigans, though I think that has changed now.
Btrfs also just works with whatever drives of mismatched sizes you throw at it and adding more later is easy. This used to be impossible with zfs pools but I think is a feature now?