From past forums reading I remember that a boot loader in Linux can have trouble booting properly when you use two different physical drives (Rather than one drive and different partitions), I think it needs to specifically get to know about both drives. Does this help ?
Your storing in password protected zip file is better than storing it plain text in a file on your computer but the password encryption of zip is probably not that strong. A friend of mine insists on using a disk encrypted pen drive with an office document having his passwords. I hope he has a backup drive :)
What’s your level of trust in their provider, netcup? For instance I would never trust anything hosted at Hetzner and Linode because they’ve been known to intercept traffic.
Interesting. Do you have sources for this statement ?
Few years ago I had a collection of maybe fifteen old disks, which I wanted to get rid of, by means of recycling. First I wanted to check the content and then format all so I put them in an external enclosure. It turned out that some disks were unusable. A closer inspection showed that these were all a certain brand and type (Forgot whether it was Seagate or Maxtor or WD). These disks would probably still do fine in a desktop or server computer (Which I no longer had at home) but not with the external enclosure. Perhaps your enclosure is the bottleneck here as well.
Arch Linux, rolling Linux distribution, would give you the newest stable software, with probably new application features, but you can use distrobox, podman-toolbox, VirtualBox, KVM (QEMU) or a live Linux cd image to play with Arch Linux every now and then, without having to install it :)