Firefox (well, librewolf, but forks are a matter of personal preference).
Chrome (Ungoogled chromium) is used as a fallback for the occasional site that doesn't work with my restrictive FF configuration.
Both have uBlock, though they're configured differently to suit their individual purposes.
Docker, using the nextcloud:stable image (not-all in-one) with postgres, behind nginx, and finally ZFS with 2x modern HDDs for storage. I run the stock apps plus a small handful, and have carried the same database through many versions over the last 5 years.
It's usable, but definitely not snappy.
The web interface for files is fine. Not instantaneous at all but not a huge problem. I have about 1TB of files (images and videos) in one folder, then varying files everywhere else. I suspect that the number of files (but probably not the size) is causing the slowdown.
Switching to, for example, the notes app is incredibly slow, and the NC Android app is just as bad.
Return for refund or replacement. If you're even slightly concerned about WD giving you trouble, but know eBay/the seller won't, just go that path since it's still available.
Since you're new, I'd recommend just using the old PC to start and get comfortable. Once you're sure you want to invest some money, you can either build it buy yourself something more energy efficient if you're super concerned about that.
As for the best OS, just any server OS will do. I run Rocky Linux which is a RHEL derivative, but you can also try TrueNas or anything else you want. Even Windows Server would work if you wanted to go that path.
There are many paths you can take, and which you go down depends heavily on personal preference and the desired use of your system.
I use KeePassXC, but am assuming KeePass is very similar.
You'll have a single file on your machine that is your encrypted password database. Syncing is not handled by KeePass and is your responsibility.
If you want to sync only when you get home, as long as your sync app that is fine with it, KeePass won't know or care.
Keep in mind if you make changes on two devices without keeping them in sync, one will probably get overwritten unless you take special care to handle it. (My sync app warns me, then I take both conflicting files and in the KeePass app, I can merge them to solve the conflict without data loss.)
It's exceedingly rare, but there's one case where a game can disappear from your Steam library: keys.
Game developers/publishers have the ability to revoke keys at any point, and that can result in games disappearing from your library.
I'm yet to hear of Valve themselves making a purchase inaccessible, but I have had keys get revoked. For example, free Gleam keys that add shovelware to your library.
Even games that Valve banned from sale on Steam can be activated and added to your account using keys. I believe that people who purchased the game also get to keep their purchase even if it's later banned from sale.
Excuse me what the fuck?
No reputable registrar requires you to run an executable on your machine. JavaScript is as far as it'll get.
I'm sure many registrars work without JS, but if I had to be sure of any one in particular, it'd be Njalla. They even have an onion site and accept monero, so they almost certainly function without JS.
At least be honest and say this post is an ad.
TLDR pls.