It's about 300mb lighter than KDE in my experiences. On 2gb of RAM, that makes a difference.
And both LXDE and LXQT use half as much RAM as Xfce.
LXDE is gonna be fine too; but it lacks a lot of the polish that XFCE has. I honestly like both for different things.
I'd rather be able to open more than 5 tabs than have a fancy UI. That's why Xfce is on my newer devices, and I install those 2 whenever someone needs an ancient laptop revived.
Just install a few of them, see what works, how much resources they use up, and what allows you to open more than one browser tab. Hell do it in a VM, Arco-B has a wide range of DE's to choose from in the installer.
It's a factor, but constantly upgrading to the newest version of software does come with risks. I've had Arch and derivatives fail to boot on multiple devices plenty of times after an update.
Some people say that they run arch for years without having any issues, but that's either extreme luck or bs.
I love to deal with problems but I don't want to waste my time.
You can usually just use a btrfs snapshot to rollback, boot, and try to update later. But there were situations when I had to use arch-chroot, and it can be problematic to install new packages in that situation.
All setups have tradeoffs, but I'd wholeheartedly suggest a stable distro like MX and nix + home-manager. It avoids all of the previously mentioned issues, and comes with other benefits. Do note that you might need to make or copy a hyprland.desktop file because home-manager can only alter files in your ~.
And I think they rewrote a bunch of C libraries in order to have a better cross-platform compiler for C and zig. Or something along those lines