1. I like Gandi. Net being euro based.
2. Not sure
3. I’d say as long as it’s got dual core with hyper threading at least if you wanna do some of those basic projects. Immich will probably be heaviest IMO. So if you can find a PC from like 2012 or 2014 even. I can run it on my old potato x220 that’s managed tolive a long strong life
4. Nah never willing to host too much.
5. Yes you can, just takes a bit more caution and just document as you go the differences. I’ve done most of mine from arch and debian

in case you didn’t already know: email has a STEEP learning curve and it’s because of how it can be captured from outside – not the technology itself.

1. dunno

2. dunno

3. If you’re tight on budget (and who isn’t), an old Android phone makes a passable server - especially one that can run Nura (used to be called PostmarketOS) - check https://wiki.nura.eco/wiki/Devices

4. Looks good to me. Be careful with email, it’s hard (yet possible) to get right. Here’s my answer to someone asking what everybody’s self-hosting: https://piefed.social/comment/12336670

5. Yes you can. Or FreeBSD, like others mentioned, or OpenBSD or Haiku OS or Windows - as long as it’s able to start the application you want to host. Some applications run on anything - check nginx. The question is what’s good to self-host on - the answer is “whatever gives you least headache”. I’m using NixOS, for its powerful text-based configuration system (store the whole OS config in Git), atomic upgrades and rollbacks. As for systemd - it’s a tool. I use it, it suits me fine. If it raises your cortisol, exercise your ability to choose - find a distro without systemd - but also remember that systemd is also a legit choice. many people (like me) are completely fine with running a systemd-based distro.

Also check out a comment I once wrote to someone asking how to get started:
https://piefed.social/comment/11341527

Where should i buy my domain and are there any things i should be careful about?

As someone else said, check the renewal price, not just the price for initial registration. And obviously try to pick a registrar that you find reasonably trustworthy.

does the end of my domain (idk the specific name but .XYZ) matter at all?

It’s called a top-level domain (TLD). TLDs are handed out by the IANA to various entities. Those entities (eg. a branch of government of a country) can set requirements for registrants and I think they also influence how much domains under that TLD cost. So you might want to pick one with sensible requirements (usually they’re pretty lax but eg. some countries may require citizenship or registering a business with them) that you’re able and willing to meet, is cheap, and that you more or less trust the managing entity of.

I get that i should use a used PC (i have none lying around), but how old?

Depending on your hardware requirements etc. and what you want to achieve by self hosting, I would suggest looking into renting a cheap VPN instead of buying an old computer. It’ll be more expensive in the long term, yes, but you won’t have to worry (as much) about things like getting a static IP address, power usage/outages, noise and possibly heat in the summer, fiddling with router settings, telling everyone your home IP address and sharing bandwidth with your server. A third option would be something like a raspberry pi, if it’s enough for your needs.

Am i willing to self host too much stuff?

The limiting factor, aside from possibly hardware if your services become very popular or are particularly demanding, will likely be your patience in figuring out how to get things working. Email can be a particularly bad one, especially if you need to be able to communicate with mainstream email services. Of course everything also requires occasional maintenance, which again takes time and patience.

Can i use Gentoo, Devuan, or other non-systemd distros as an OS?

Sure, why not? But for a beginner I would recommend picking something with a good amount of documentation and support available to make finding relevant information easier and to (hopefully) be able to rule out the choice of OS as a potential cause when things don’t work.