Took me a few decades short of 200 years, but finally managed to move from being a one-county state (one, plus Venice). And, eventually, into a quite decent world power.
Partially because of me, as my Chaplain brought the first contemporary Catholic heresy of Fraticelli to the world, to which my then-ruler briefly converted (as in, long enough to convert a bunch of family members and nobles, but not long enough to be HW'd into oblivion), and partially because the Pope was basically Hugh Hefpope, a fuckton of heresies started springing up and spreading. Aside from Fraticelli, who didn't get much of a foothold in my home turf but eventually converted the Italian king, there were also a bunch of Cathars northwest of Alps and a Waldensian heretic discovery by my Court Chaplain.
The Italian king got a revolt by nobles in the bunch of northern counties near Alps but also a couple of Croatian counties in Italy.
Then still Catholic, I managed to Holy Warinate the region under me before the war ended. Then aforementioned Chaplain did his thing, and my insane master administrator Doge had become Waldensian. He was succeeded by a guy who was so adept at sleeping around he actually got a temporary thingy I didn't even know existed, 'Court Tomcat', and promptly seduced the Italian, Byzantine and Bulgarian (because the latter were blobbing HARD) queens, in addition to a whole bunch of his other paramours. And got them pregnant. Like, all three. And didn't get caught.
As a fellow Heretic, albeit Fraticelli, Italian king for the most part pissed off, and so began my expansion northwards. Luckily for me, the Mad Accountant Doge's successor's son was trained in Martial, becoming a Brilliant Strategist and, thanks to his leadership during the first campaign, a Light Foot Leader and a Siege Leader. And, of course, a Waldensian. And when Doge Juan (I don't remember the actual name, but it was most likely Cosimo. I had at least three Cosimos in a row as rulers. Must be popular.) died, he took over.
At one point, the Bulgarian king randomly asked to marry my half-sister, and since he was powerful, and the sister had shit stats, I send her off to him. The guy later turned out to be absolutely *crucial* in saving my bacon with his 10k armies or picking of skirmishing armies. Completely unplanned.
By the point I quit, he conquered the entire area of Italy east of Venice (with the Venetian-Italian border at Aquilea) south, to Nuremberg north along with the entire part of Alps on the opposite side from Italy. So now I border Germany in the northwest, mostly regular 866 start area, Bavaria which right now is pretty much actually Prague, Bulgarians and Byzantium, and touch a single Polish county.
Also, for some reason, almost all armies I can see are hostile, even though I have no wars declared. Which resulted in much hilarity; once, as France, Germany and Burgundy were 'defending' from a Braunschweig's invasion by Vikings... by pooling a 13k doomstack IN THE FUCKING ALPS - which I tried to break apart in preparation for my invasion of Bavaria after the last truce ended... only to discover they had another doomstack of 17k who wiped the floor with the troops I sent, eventually breaking up as the kings ran out of dosh...
...then again as Italian king, who happened to be a genius, tried to pull his bullshit on MY AQUILEA, YOU BASTARD, only to discover he had all the peasant revolts explode on him. There were at least three different ones, all at once. Which I helped, tactically, by sieging different fiefs than they were interested in and a LOT of manouevering around.
I also discovered you can rename dynasties which are not yours, which has led me to renaming the Serene Republic, which was all-but hereditary thanks to my +30 gold per month and like 2k in vault, so noticing my dynasty name (which was RNG) I now lead The Glorious Serene Republic of Ariostotzka. 'Glorious' is the adjective.
And all I will say about this is you will want to try changing yours to that.