LXQt, XFCE, Maté, TDE. Any of them will do. Which you choose depends on personal preference and how large an ecosystem you want—LXQt has only a few basic applications, TDE has pretty much everything that was in KDE3, the others are somewhere in between.

You could try Niri. I have tested it with a ~10 year old notebook with a 1st gen Core i5 cpu.

But, even newest Gnome runs smooth on this machine.

Moksha Heck, just install Bodhi Linux 7, your choice between Ubuntu based or Debian based.

That's a reasonable machine. You probably could use anything but if you want lighter weight you could use Xfce4. If it is a laptop you could use stock gnome with some swap as a backup to prevent OOM

In my experiments with a similar setup and integrated graphics, full-wayland Kubuntu feels much more responsive than Xorg-Lubuntu, for what it's worth

If the PC has an SSD, install anything you want, the PC will handle it fine.

Ironically, ChromeOS Flex would run smooth on those specs, since it does so on my dogshit Samsung Chromebook 3 with shittier specs.

river or sway