Suggesting NixOS to a completely new user is stupid. NixOS is cool but very different from almost all Linux distros. Comes with its own language you have to learn as well.
Thing is. Mint is for the most part a just works distro. Based on Ubuntu it is very easy to find help for it. Combine that with a load of sane defaults like disabling snaps. The default UI and theme could defiantly use a facelift
For music. I use navidrome. It works a load better then jellyfin for this IMO. You can use the same file location for both jellyfin and navidrome if needed.
It not only hurts tor because it usage up bandwith but in other ways as well. Torrenting makes many peer to peer connections which hurts tor in multiple ways. I suggest reading the docs of tor to better understand how and why this is.
I dont understand your question about I2P. You need some form of I2P router to use I2P in anyway.
I have used SAP extensively. The issue is SAP can do soo soo much more then many ERP systems in regards of finance. It is a nightmare to use but one of the only systems capable of what it does. Also it doesn't help that it is over 50 years old at this point and companies are stuck with it. It is no easy task to migrate that kind of data.
Sounds like you are a data hoarder haha. Can't blame you. But for such hobby's perhaps a ZFS system with deduplication and a second ZFS system to use for backup of the first system is what you want.
Ahh I see yes that's better.