Don’t be intimidated by all the DLC, wait for a while then only buy what you need to expand the game in the way you want to play.
Read the CK2 wiki beginner’s guide, learn to play in 1066 Ireland.(AKA Tutorial Island) and don’t ragequit when things go wrong, losing is how you learn.
And when you get bored of Mediaeval Eurasia, play in Westeros instead.