Decided to have another crack at one of these records, very well pleased with the result!
The most interesting starts for the crusaders are when the Buyids managed to collapse the Abbasids. This doesn't happen all that often, but when it does it leaves the near east in a much more interesting state, with most of the wonders unbuilt and especially the Spiral Minaret. I eventually got one of these starts, and decided to attempt to make Tarsus my capital. It worked.
Here's an early screenshot after the flip of Edessa/Antioch:
Also razed Sis. Start research on Assymetric Warfare for the free Great Spy. Tarsus built a Work Boat (with some chopping) followed by Spiral Minaret. Antioch built enough Catholic Missionaries to spread Catholicism to all of my cities, as well as a settler to found Coxon to the north of the ruins of Sis. Edessa (and later Tripoli too) built additional Trebuchets. Tarsus later built Narekevank also for the free Priest specialist and was my Great Saint factory for the game, in between building the occasional missionary.
Next target was Rebel Tripoli, followed by the razing of Hom and Damascus. While it wasn't my target, seeing Tyre controlled not by KoJ but by Yemen and defended by only a single Skirmisher was too hard to resist. The final city captured in the early stages was Rakka (that's the Zengid name, can't remember what it's original name was). Then time to heal all of my troops and send the siege units and Sword/Axeman units south to attack Jerusalem and the Norman Cavalry up to Edessa to repel the Zengids.
An important step was to declare war on the KoJ a few turns before the Zengid spawn. Whilst this annoys the Christian civs, it doesn't make them so upset as to close their borders. But what it does allow is the Islamic civs to open their borders to you! Instant UHV condition met, with Abbasids, Seljuks, Fatimids and Rum all signing OB agreements.
Did some one-sided trading for cash with Abbasids to get them as pleased as I could (Cautious I think it was) before the Zengid spawn. And this did the trick, with the Zengids starting at war with the Abbasids (as well as me). Crucially, this means that about half of the Zengid cavalry units get tied up fighting around Mosul against the Abbasids.
Quickly retook Rakka, then killed all of the Zengid units which were outside of city borders (quite a few actually). Brought up the newly built Trebuchets from Edessa and Tripoli towards the Zengid capital and softened up the defenders for a while. After killing most of the defenders in the capital (but not all of them), the Zengids were willing to capitulate - which I accepted
In the meantime, my southern troops took Jerusalem leaving the Kingdom of Acre with just Acre (Gaza had been captured by the Fatimids). Because Acre doesn't start with Catholicism, KoA switched to Orthodoxy. After chasing down all of the KoA units outside Acre's walls they capitulated too.
In order to stablise the KoA, I then declared war on the Fatimids and returned Gaza to my vassal. I wasn't planning on waging a big war against the Fatimids, but when I realised that their ongoing war with the former KoJ had weakened them to the extent of not having any attacking units left, I decided to try and capitulate them before the Ayyubid spawn.
I rushed the northern troops down as fast as possible and captured each of the coastal Fatimid cities in turn. Softening up Cairo for a while and eliminating most of the defenders was enough to get them to capitulate, just before they collapsed two turns later - in spite of my returning their cities to them. Anyway, the 3 vassal victory condition had been met.
Most of the remainder of the game was spent building Christian Missionaries as quickly as possible and generally increasing the number of Catholics in the world. Rum collapsed after losing all but their capital city, which I took from the Rebels just before the Byzantines got to it. I captured Medina and gave it to KoA and captured Mecca for myself ($$$). My Zengid ally captured some of the Rebel cities in Egypt just before the Ayyubids spawned and were duly crushed into submission by my troops.
I only used one Great Saint to convert cities (used him in Mesopotamia) while using regular Missionaries to spread Catholicism to the most populous Byzantine/Armenian/Egyptian cities.
I forgot to use my Great Spy to trigger a Golden Age until right near the end actually - probably should have done this much sooner and I reckon would have managed a better time if I had. My second Great Saint was one turn away from spawning in my capital when the URV was triggered.