Linux

As this is your first go, I'd recommend not tinkering with USE flags at all. Take the defaults, find what you don't like, and consider tweaks later. USE flags can end up like a sort of "dependency hell", with one package not working correctly because it expects another package to have something you've excluded. It's uncommon, but frustrating when it happens. It's best to start with the defaults.

My advice would be to not overthink things. Whatever you do, there's always a way to undo and/or change it

A few personal notes here https://wik/ i.gardiol.org/3-linux-gentoo see the su pages as well

Gentoo is a great choice! I use it an all my devices from servers to laptops and workstations . It's fun, solid, stable and efficient.

Good choice, and... Good luck... Dm for any issue.

Not that I'm trying to dissuade you, as I am on Gentoo and have been for about 1 year now, but if you're only interested in other init systems, did you consider trying Artix?

I'd still say go with Gentoo if you want fine grained control over nearly every aspect of your system, as compiler flags, eselect profiles, and just overall minimalism make it superior for tinkerers imho.

That said, if you just wanted to experience other init systems like openrc, then Artix might be a good option. Prior to jumping to Gentoo, I was on Artix Linux with runit init system for 6 years. It was good, but I wanted to know more about Gentoo. There were some definite tradeoffs from Artix with runit, but I appreciated the fine grained control I got with Gentoo's compiler flags, so I stayed on Gentoo.

The only advice I'd say when installing Gentoo is to choose your profile carefully during initial install and to choose your stage 3 tarball accordingly (just think about your ultimate use case). Also, if you need to use wifi, make sure to install wpa supplicant while chrooted into the live environment.

Anyways, hope this helps.

For 1: As a beginner keep away from global use flags, stick to per package use flags. Global use flags can make things very complicated.

You can (and generally do) install gentoo in a Chroot, I recommend using btrfs with subvolumes on your current install, then switching when everything works, that way you can roll back.

But since you're on arch you probably already know a fair chunk of what is necessary.

1. Use flags are more about features, there are other flags like cpu architecture. I don't recommend you do too much on your first build, except for having some sweeping ones like X and/or Wayland. Then once you have it running you can do a rebuild. I also recommend taking subvolume snapshots before doing major changes.
2. Yes. https://wiki.gentoo.org/wiki/OpenRC#Runlevels

Any advice from people that already use Gentoo? Especially things that they wish they knew before trying for the first time?

This is more things-about-bootloaders I wished I'd known/remembered when installing more recent systems, but:

• If you want to use GPT partitions on a system with legacy BIOS boot, remember that you will need an additional unformatted small partition at the beginning of the disk (this tidbit of information used to be in the handbook, but has been removed)
• If you're trying to install GRUB on a UEFI system, and it looks like everything should work but the system fails to boot, read the troubleshooting section of the GRUB page in the wiki for information on how to handle defective UEFI implementations.
• Do not try to enable Secure Boot if this is your first rodeo. Get the rest working first.

How much time and effort should I put into fine tuning the global USE flags if my initial goal is to get a system up and running?

Not much, unless there's something you really want to exclude (-systemd, for instance). Most of the time the default USE flags will give you a workable, feature-rich system (and allow you to use more binary packages).

What you need to pay attention to is your choice of profile, which sets your default USE flags. Profiles in the desktop series enable a lot of USE flags. For the most basic command-line system, you're better off picking default/linux/amd64/23.0 (or default/linux/amd64/23.0/split-usr if you want the old FHS setup where /bin and /usr/bin etc. are different directories—if you don't care about this, stick with the default and ignore split-usr). Avoid no-multilib, hardened, and anything marked "(exp)" or "(dev)" unless you have some specific reason for wanting that profile.

With systemd, I enable --nowed that which I wanted to “autostart” (iptables and sshd, for instance). Is there an equally intuitive counterpart with OpenRC?

I think you want the rc-update command, specifically rc-update add [service] default (assuming you want the default runlevel, which you nearly always do). There's a man page.

After 15 years on arch, last year I looked at Gentoo, artix and void. I chose void and have no complaints. It's a very unopinionated distro, uses runit, rolling release, nice package manager, and works well with just compiling packages you want from source. My arch was heavily optimised and clean, but runit is so simple to use and boot times are insane. After post, my boot is around 3 seconds. Shutdown is about 1-2 seconds.

https://youtu.be/9PnXcP8ZI7M

There is absolutely not a single reason to use Gentoo, unless you have a really old PC that you really, REALLY need to use it.