In layman’s speech (my speech) raid 1 and mirroring are essentially the same thing.
Technically, IIUC RAID is only used for hardware raid controllers, ZFS calls their equivalent RAIDZ1 (and I think it stores data in one disk and parity in another?) and both LVM and btrfs call theirs mirroring (each with its nuances). Whichever you pick, it’s a mode where you use two disks at 50% efficiency and your data survives the loss of one disk.
There are configurations that use more disks with higher efficiency than 50%, but I would avoid them in a homelab because the more disks you have, the higher the power drain and the higher the chance that at least one of them will fail, and in a homelab scenario you really want to minimize the change of needing to perform maintenance (replacing a drive in a RAID and restoring from a backup are both a hassle).
In your shoes (and in mine, whenever I’ll need to redo my RAID1 NAS), I’d skip RAID altogether and use the extra disk for extra backups of the data I care about.
Most of my NAS is filled with movies I’ve ripped, and I honestly wouldn’t really care much if I were to lose them: the movies I may want to re-watch are really few and I can just rip them again (or even buy them again) if the need arises.
Backups are enormously more important than RAID (will RAID do anything for you if you accidentally delete your family photos? what if the NAS floods or gets dropped on the floor?): you should really direct your time/resources/effort towards setting up automatic and monitored backups before worrying about RAID.


Letsencrypt works fine, just use a “real” domain and DNS challenge.
Your service will need to be on the “real” domain, but it won’t need to be accessible externally and you won’t need a public DNS entry for it (of course your VPS will still need to be able to resolve the backend’s name).