Setting up
First up, found Cairo and Domyat as they are obviously integral to your economic and industrial base.
Use your third settler to found Aswan in order to grab Upper Egypt for UHV1. It will take a while before the city is up and running, but it will eventually be among your best cities.
In previous games where I had settled Al-Minya rather than Aswan I found Makuria would without fail DoW on me whenever they could. Settling Aswan seemed to negate this for some strange reason (or maybe I was just lucky?), but make sure you keep your defences strongest here just in case. You don't really need many troops in Lower Egypt for the time being, and you also don't need Merkurious getting ideas while you're getting ready for KoJ to spawn.
Build at least 2-3 workers in each city, you don't have time to waste getting your tiles improved. As has been said, send your Berbers around to Hejaz, nicking any rebel workers you find on the way. I believe there are scripts to ensure Medina and Mecca flip to you, though I'm not sure on what conditions, at the very least you have to go and actually visit the cities I believe. Medina's forces were too strong for me, but I killed a couple without losses and went down to Mecca. Taking Mecca at the loss of one Berber, Medina subsequently flipped (possibly due to combat influence from the earlier victories?). In any case, you now have Hejaz for minimal investment, meaning you just have to claim the Levant now for UHV1.
UHV1 - Halfway there, just take out the Crusaders
At this point it's all infrastructure and improvements. Make the obvious choices before gearing up to invade the Levant. I started preparing around 1050, with Cairo (mined) and Medina producing the bulk of my forces (plenty of trebs, Berbers). Alexandria and Domyat can make nice contributions of axes and spears with the few hammers they have. Mecca and Aswan should still be too underdeveloped to contribute significantly.
KoJ should be a cakewalk with enough trebs (min. 4). I dialled down science for a few turns to hire a few mercs as additional fodder. My preference is to let KoJ found Aqaba (and save me having to build an extra settler), which they should do as long as Tyre and Acre are both existent. Hopefully they will have sent a few units on a futile attack by this point, making your life a whole lot easier. A quick sweep will net you Transjordan and Palestine. I got even luckier and KoJ wasted even more troops taking Damascus, meaning that was easy prey as well.
PoA is a bit of an unknown quantity and what they do depends to a large extent on who their neighbours are. In my case they seemed to thinking thumping me while I was fighting KoJ was their best bet, so I quickly brokered peace as KoJ was the immediate threat. Try not to mess around too much taking their cities, you have a time limit and you also don't want to be DoW'ing on anyone else if possible. In my case PoA survived as my vassal in "the County of Edessa". Once UHV1 is checked off, you can liberate their cities back to them (in my case I liberated Antioch, Tripoli, Homs and Ar-Raqqa) to reduce costs/stability and form a nice buffer.
Whilst you're doing all this fighting you should be focusing on infrastructure, because once you've completed UHV1 you'll need to be preparing for your invasion of Iraq while at the same time getting UHV2 complete.
UHV2 - Missionary Mania
Try to build as many missionaries as possible. The earlier you can trigger that golden age from UHV2, the better you'll be able to prepare for the Abbasids. Spreading Shia to the big Byzantine cities that are likely to only have Orthodoxy helps a lot. If Merkurios manages his cities well enough they're going to be nice large cities you'll want Shia in. But otherwise spread wherever you can, grow your cities as large as you can afford, and if necessary use persecutors on any of the bigger ones with only 1 or 2 other religions (I only ended up persecuting Sunni from size 16 Domyat, leaving Shia). Great Saints probably help, but I didn't get any in time sadly.
UHV3 - Mesopotamia and Jihad
Build Trebs ASAP. I probably had about 12, with another few and a bunch of cats later on, when I began my invasion of Mesopotamia. Hire a whole stack of Mercs as you'll need a lot of fodder, and hopefully you have a truckload of Berbers. I didn't end up needing the cats in the end as I caught the entire Abbasid army in the middle of the desert trying to spring a surprise attack on the Levant.
Chances are you wont collapse the Abbasids before they manage to call a holy war (assuming they can). In my case a bunch of Sunni factions DoW's on me. Ghaznavids, Ghorids and Oman were all obviously too far away, although I could've done without losing the trade routes. Conveniently the Seljuks were busy with the Byzantines, Georgia and the Mongols, though on an alternate playthrough they completely wiped out my forces when they were just dealing with the Mongols. Rum is probably your main concern, although hopefully they're fighting someone else. At the very least they'll also be dealing with Mongols, wont have so many troops that you can't send in quick Berbers to harry them, and you'll have PoA as a buffer still hopefully.
Collapsing the Abbasids can be a big ask. I had to take them all the way down to Kufah and Wasit before they did.
Other notes:
Makuria vassal'd after a brief war while I was fighting PoA. Yemen also vassal'd after they had finished off the Zengids. Only Antioch really helped in any significant way, although the Makurian and Yemeni troops often provided a distraction for the barbs that spawn in the Arabian Desert.
Always have enough siege weapons when invading Iraq. While you can build more after the attack begins, the closest cities like Jerusalem, Damascus and Homs are already quite a trek from where your frontline is going to be, so make sure you take enough with you in the first place to keep the momentum going. You're racing against the clock on both the UHV, and potentially others joining in on the Jihad against you. As soon as you collapse the Abbasids and take Baghdad, the game should be over.
Build Berbers in every city once any more infrastructure is pointless. They are fast, both on the roads around to Northern Iraq and even crossing the Arabian Desert.
