Very late replying to this, but maybe it'll be helpful for someone.
Yes, the base game is enough, but I'd highly recommend getting the religious DLC (The Sacred and the Profane) if its also on sale (as it is now until April 26th).
This was recommended to me and I'm glad I took this advice. The base game has a lot of events, but the additional events and content from the religious DLC really provide a lot of good flavour to the playing experience.
I'm planning on buying the Behind the Throne DLC tomorrow (after I hopefully finish up my current game) to add more some dynasty-related events, and Heroes of the Aegean for the extra playable nation. But the sense I have, from the reviews I've read, is these have less impact than The Sacred and the Profane DLC, which is insanely good value for money.