Don’t be afraid to try out CachyOS’s Niri implementation. In in its current form it’s pretty unique compared to the other WM choices on the list in the fact that it runs an opinionated desktop shell out of the box. This shell, Noctalia, gives Niri a near desktop environment like experience and might appeal to you.
Do use all of the above at your leisure. pacman is the base package manager of Arch Linux. paru is an “AUR helper”, that allows you to make use of the AUR in concert with the rest of the package system that you maintain with pacman. Octopi is a graphical front end for both of those programs. You can toggle between the two with the green alien icon in the top bar.
Don’t use anything else. Unless you also intend on using Flatpaks as well(though there’s rarely a reason to given the software selection provided by the AUR).
I would personally just stick to managing Flatpaks with the command line, but graphical utilities like KDE Discover do exist they just need to be used with care. As long as you don’t install its optional dependency packagekit-qt6 you’re safe.
Do use Limine or GRUB combined with your filesystem using btrfs to have the installer automatically configure bootable snapshots for you. Whether you choose one or the other is largely a matter of whether you want to encrypt your boot partition, but the full list of features can be found here.
Since you don’t need /boot encrypted, the default selection of Limine sounds like what you’re looking for.
If you select the box to encrypt your system partition in the installer, it will be done with LUKS2. This should not fray your nerves.
Don’t expect a Debian-like experience immediately. It will likely take you a little time to adjust to the rolling release update lifestyle and there’s really nothing you can do to avoid that. Once you settle in and understand updating then everything calms down once again.
Don’t update too often. This is a frequent mistake that people migrating from other distro families make, exacerbated by update utilities(like cachy-update) that give you a pesky tray icon nagging you to update since you almost always have pending updates on a rolling release system.
While useful elsewhere, since you now have the potential to be updating hundreds of system packages that are frozen on other distros, updating too often increases the chances of broken packages that might present as much more serious situations than they really are.
Also if you updated every time there was a new version of anything, you’d drive yourself absolutely crazy. Seriously.
It’s best to update on a cadence. My suggestion would be every 1 to 7 days.
Don’t panic if something breaks. The drawback of bleeding edge rolling release is that occasionally things are going to go pear shaped. The advantage is that you’re using bleeding edge software, and when things do break they get fixed quickly.
If you’re not feverishly updating your system, it’s likely software you use will suffer regressions and you’ll never even know it since they were fixed within the same update window. This is why it’s useful to update when you’re about to stop using your system for at least a few hours. If you start using it again and something is wrong, often the fix is as simple as updating again, as time has already elapsed since something went wrong.
And if not, then that’s what snapshots are for.
There are pros and cons to rolling release, but the cons are well mitigated and once you fall into rhythm with it, it’s not nearly as frantic as it seems.
I could probably go on but I’ll stop for now.