I do wonder how much higher that would be if GPUs targeting 4K were £299 rather than £999.
Although some of it is down to monitors being on desks right in front of you and 4K not really being needed. It would also be interesting to for Valve to weight the results by hours spent gaming that month (and amount they actually spend on games), rather than just counting hardware numbers.
The first is a bit rough. It got a remake with Black Mesa which used to be free, but I don't think it is any more.
I'd honestly just start with 2. It's a better game all round. You can always go back and play Black Mesa later if you like it.
If you have a VR headset and a decent rig, Half Life Alyx is well worth it. I'd definitely play HL2 plus Episodes 1 and 2 before heading into that one.