Welcome to paradox strategy games; you thought SSI stuff was hard, you poor fool
On a serious note: CK2 is increadably fun, and remarkably simple - assuming you go through *ALL* the tutorials. You're gonna have to read a lot before you start playing - just be thankful it isn't CK1, or EU3 neither of which have any tutorials as such. Prepair to fail horrifically your first game. Read the entirety of the CK2 playthrough on this very site if you haven't already, it drops a good overview in amonst the creative licence and storytelling.
As far as difficulty goes - you want a small nation to start out so you're not overwhelmed with options, but not so small your military options are a small rabbit or a bloke with a dog called rovér. My advice would be the Duke of Gwynedd. You start with 2 or 3 provinces, a full court, no major wars, your family is prestigious enough to marry off to royal family's children, and with a couple of swift wars to the south and some buttering up of the Duke of Powys (assuming my memory is correct) it's possible to become King of Wales inside the first ruler's lifespan if luck is on your side.
And if all else fails, send me a PM with your steam name and I'll see if I can provide some advice; I've been playing a lot of CK2 recently