Well, it ended up being pretty close but I finished my the one tag, one culture, one faith, all provinces, world conquest with the Teutonic Order. Phew! I'm glad I did this because now I won't ever have that nagging urge to "do it all" again on a future playthrough and I can have a more regional focus and not always be so completely warlike.
One culture is definitely a bitch. I almost didn't have enough diplomacy to get it done in time, even though my WC was over in 1760. However, being able to exploit one dev in every province provided me just enough of the edge to squeak past, though it was hell on my fingers and hand. Those goddamn European cities with 50+ dev were awful (since nothing reduces culture conversion time) and I didn't really have the admin points to concentrate dev and/or move the capital to a low dev province to be able to concentrate more dev. The last blitzkrieg of war was pretty fun, though. I had so much money I went 800+ over my force limit and made 50-100+ stack armies to steamroll everything. So much manpower the attrition didn't matter at all, especially given how quick the sieges were.
My idea groups were Divine -> Religious -> Administrative -> Diplomatic -> Influence -> Horde -> Espionage -> (Drop Influence) Humanist -> Expansion. Outside of one difference, it's really hard to imagine picking any different ideas. I suppose I could skip Divine but there was a TO mission that required a MIL tech, thus the choice. In hindsight, I really should have gone with Humanism earlier, definitely before Espionage (which I chose for AE reduction and siege ability). Taking years off separatism was a big light bulb moment and really made going way over 100% OE super manageable. I'm not sure I could have taken it before any of the others simply because they're just so powerful; maybe Humanism before Horde would have been optimal but at the time I had a ton of MIL points and was always low on admin. The other big light bulb moment was not ignoring trade companies and fixing/understanding my trade situation during the mid-game. I went from barely scraping by financially with a a handful of loans often to being totally in control financially in the space of about five years, all just from fixing what I already had. If I had been playing that correctly from the beginning, I'm guessing I could have finished 20-40 years earlier.
I was the Teutonic Order, Mongol Jerusalem, Poland, then the Lithuanian-Polish Commonwealth. It was my first time doing that kind of elaborate fuckery so it was a lot of fun. Actually having worthwhile missions to do during the entire game instead of just the early/mid game made things a lot more fun for me. The Commonwealth had some absolutely killer missions to push me forward at the end, particularly the 15 years of -15% CCR, +25% culture conversion attached to the ruler, and 5 reform for every university. I pumped universities before finishing that mission and ended up with 1800 reform so I could quickly finish the tree (a blob campaign means slow reform progress) and also switch out some earlier reforms as needed.
Great campaign and still so much EU4 I've yet to explore.