"what recorder should I buy/dowloand?"
I recommend OBS. It's free and works very well. Definitely wouldn't recommend buying any software for capturing PC gameplay considering the amount of free options.
https://obsproject.com/

"Also i noticed that there isn't any Crusader Kings 2 speedrun, so... I'm the first?"
There are a few CK2 speedruns, not sure if there's anything like what you've described: https://www.speedrun.com/ck2

Calling it the "hardest speedrun ever" when you haven't even done a run of it (or any game, for that matter) is very questionable.

Speedrunning

Off-topic discussion, unrelated to speedrunning.

Talk