Your problem is that you’re starting from the wrong premise: the primary goal of most people working on Linux is not to make more people switch to it, strange as that may sound, it’s to create an operating system that they personally want to use. Which can mean a lot of different things, depending on the person. So it’s inevitable that there are a lot of different distros, and the only reason there aren’t even more is that most of the one-man shows that don’t attract many users peter out and vanish after a few months or years.

Assuming you mean 2GB RAM, it will run a full Linux. I was using a 2008-vintage laptop with similar specs as a secondary machine until recently, and it was capable of handling many light workloads. Retro gaming up to the 16-bit era should be fine. 720p video playback from local storage (never tried streaming) was fine. Modern websites were very hard on it, though, so I didn’t normally use it in that capacity.

Just pick a distro that isn’t too bloated, and a desktop environment that’s suited to older machines and doesn’t expect too much of the hardware, and you’ll be fine.

(My laptop still works, by the way. I gave it up because 1. I got a good deal on a machine with much higher specs and 2. I run Gentoo, and compiling a modern version of GCC on a dual-core of that vintage takes longer than you would expect.)

Actually, it goes to a lot of trouble not to step on the toes of later versions of KDE, and there are people who have them both installed side-by-each without major problems.

-nolisten is an actual option passed to the X server—your distro may do so by default—to work around a known security issue in some versions. I admit I’d have to look up the details, as it’s been a couple of years since that issue was reported. Recent X versions almost certainly have a patch.

Gentoo works best for me because I’m a control freak. It lets me tune my system in any way I want, and I don’t mind leaving my computer on while I’m asleep so that it can compile its way through libreoffice, webkit, and a couple of browsers. Plus, based on complaints I hear from people using other distros, Portage beats other package managers in every way except speed.

This doesn’t mean that it’s best for everyone, mind you, just that it’s best for me.

There are no open security bugs against TDE that I’m aware of—if there were, I’d expect them to be fixed in the next release. In my experience, the development team, while not huge, is active and competent.

I’ve been using TDE since a little while after Gentoo sunsetted KDE3, and I’ve had no issues. Just make sure your X server is secure—-nolisten and all that stuff—and don’t try to use Konqueror as a web browser (it remains an excellent file manager), and you should be fine.

Wayland is “more secure” than X in that it makes less LAN contact by default and tries to sandbox programs from one another to an extent, just in case some future browser exploit that can copy random swathes of your screen tries to screenshot your password manager or something. There are no active exploits against a correctly-configured X server at this time that will magically vanish if you switch to Wayland, as far as I’m aware—it’s more future-proofing stuff.