Again you've taught me something I didn't know.

Dublin has always been a pain in my ass. In the early game I find I cannot afford to send my main/2nd army to sack something as remote and largely useless as Dublin, but I do it anyway and shrug off the waste of time. The fact that there are no city walls actually makes it harder unless I have a horde of troops because pinching off their sally at the gate is my specialty.

So... it was you that I heard the purchase settlement trick from, much gratitude. I've had to include that bit of advice to anyone I think is worthy of it because it basically doubles your empire on turn one. Very nice tip.

I Note that as a western christian faction, you can decimate the Moors, Turks, and Egyptians with your first crusade. Get perfect relations with the pope and on that same turn, request a crusade for Baghdad.
Ouch!

Then, ignore your crusade target and head toward the Moorish territory. Use the tips I presented for not losing troops to desertion. It's best to get a bunch of captain promotion/adoption generals to bolster your family first.

Smash the Moors within a few turns, and then split your forces.

2-3 stacks should head toward Alexandria, Egypt, and the rest should head to Byzantium/Asia Minor.

If you feel like it, take out the Byzantines on your way... but remember your 10 turn join/leave crusade limit has probably been reached by the time you attack. Which means your troops have to be guided missiles. If you cannot beseige/sack a city in 2 turns and then move on without losing troops to desertion, let a straggler general/stack get it and keep moving.

You may not be able to smash every single Turkish city, but you will cripple them, utterly destroy the Moors, and leave Egypt with at most, Jedda as a province. You should be able to take Egypt and Syria without losing too many troops.

If you sack all castles and exterminate all cities, you should be able to leave minimal garrisons. But frankly, if they revolt, you don't care. You've eliminated all 3 Muslim factions and sacked a lot of cities. Expect to keep all castles no matter what (recruit garrisons as they become available), and keeping cities is recommended whenever viable.

I recommend the train method for converting Muslim lands.

Start whereever your conquests are closest to your faction. Spam 5-10+ priests in your border city during or after your invasion. Then send them single file, on a non-stop tour of the Muslim territories. Each region you are in should gain 15% or more catholocism per turn until it reaches nearly 75%. You will probably get cardinals this way.

You can afford to dawdle a little in regions with cities as opposed to castles, but keep moving from (I recommend) Spain to West Africa, North/Central Africa, Egypt, the Holy land, and then Asia Minor.

This tour may occupy the priests entire lives, but you are sure to get a few cardinals for your trouble and viable colonial states in Africa and Asia.

If you'd like a quick return from the crusade, be sure to build up a decent navy on your way there. (The only thing I really use navies for).

Then send several clusters of your armies back on clusters of ships, avoiding pirates and strong navies. You can get back from your long crusade and even begin an attack against your rivals on two fronts; from the direction of your homeland and from the east. Or you could simply conquer Hungary, Poland, and the HRE on your way back.

I find that massive crusades usually involve massive loss of florins/turn afterward. But keep your armies healthy and keep sacking cities, and you can nearly keep your budget afloat or at least not too terribly in debt until the next crusade.

Then, have everyone join up again... by the second crusade, you should not have to deal with massive deficits again.