No problem posting about CS Lifthrasir- I was already thinking about CS for the 7th part of roster expansion in the next update- Mercenaries and AOR.
The main issue is that costs of unit are reflected in EDU so for every unit that we make 'mercenaries' it requires a specific slot in the EDU so making 1 version mercenary and 1 version regular is 2x the slots used. Also from historical perspective not all mercenaries are the same. There are companies of mercenaries completely paid for on contract or serving individually in such numbers full units can be fielded. Just as Normans originally served in southern Italy as individuals, then small groups, then even entire families moved from Normandy to Sicily as Guiscard carved out a Duchy and then it became a Kingdom. Many rosters already reflect 'mercenary' units such as Varangian Guard, Scots Guard, Christian Guard, etc.
So I've wanted for awhile to better reflect the types of mercenaries available in game with basically 3 main variants;
Mercenary companies- these would be small in number at game start and use the mercenary pool for recruitment. Such units are recruited in the field and are the typical contracted mercenaries. Besancons, Gascons, Irish Kerns, Galloglaish, Saxon Axemen, Landsnechts, Viking Swordsmen, Flemish Pikemen, Swiss, etc. Starting in 1200s such units become increasingly common and the heyday is between 1300-1500 so majority of famous units like Swiss and Landsnechts become available in late 1300s or early 1400s. Such units can be replenished anywhere its mercenary pool is active but if recruiting Swiss in Italy and traveling to Anatolia for example the Swiss would have to be sent back to Italy to replenish.
The next type are mercenaries available from a mercenary barracks or AOR and are mostly AOR restricted recruitment even from mercenary barracks but with a structured system in place and often in a vassal or client relationship with the faction in question such as; Armenians, Alans, Turkish archers in Sicily, Turkopoles, Pavise Crossbowmen, Bedouins, Arab Cavalry, and many others. Mercenary barracks might be expensive to build and cause some unrest but in many areas hugely expand the number of units available. Also once a unit is recruited in the mercenary barracks often it can be replenished anywhere in its AOR not having to travel back to the barracks to replenish.
Finally the last type of mercenary is actually integrated into faction rosters such as; Scots Guard, Latinikon, Skythikon, Chude militia, Pechenegs, Scandinavian Guard, Christian Guard, and a handful of others so such units are available wherever the right building is when controlled by the faction in which roster the unit belongs.
There are a very few additional units which require a specific region to be owned such as Constable of Jerusalem, Varangians, Scholarii, Knights of Jerusalem, maybe some others I can't remember. Right now I'd suggest removing the hidden resource region Jerusalem and making Constables and Knights of Jerusalem max 1 available and just require Capitol hidden resource and Crusaders ownership. Eventually CS might conquer other capitols but could never have many available anyway because of the 1 limit. Similarly with Varangians and Scholarii.
I am not sure if I got your meaning about Western support for CS Lifthrasir... I take the events as the Kingdom of Jerusalem was strongest between 1st and 2nd Crusades and while it received suppport from Europe it wasn't reliant upon such support until after 2nd Crusade. After losses during Egypt campaigns and the failed 2nd Crusade the Kingdom of Jerusalem needed more and more European support... primarily the Knight Orders began to take over more of the defense while calling a Crusade became almost necessary to have much chance of large scale offensive operations. This is not strictly about falling fortunes of Kingdom of Jerusalem and the northern Counties but also the fact that Muslim factions which had been divided and warring against each other were united first by Zengids and finallly Ayyubids under Saladin securing Syria and Egypt which allowed Muslim control of Jerusalem for rest of the medieval era by treaty when the 3rd Crusade ended. All Crusades after the 3rd failed to accomplish much in Holy lands though 4th Crusade wrecked ERE.
Basically the Knight Orders were most interested in defending Jerusalem so Jerusalem, Acre, and Tyre were their main garrisons (secure ports of Acre and Tyre to receive shipments from Europe while Jerusalem was too exposed to both Egypt and Jordan and required strategic castles to be defended. European Crusader volunteers generally arrived in large numbers only wanting to attack Muslim and heathen lands and were less interested in steady defense of the kingdom's already held territories outside of Jerusalem because such defense did not offer huge loot to offset the costs of the journey and was also a much longer route to spiritual purity than fighting and killing in Crusade as blessed by the Pope compared to guard duty.
The result was almost all the Frankish settlers and many of the converted Christians plus many Syrian Christians were exposed to Muslim retaliatory raids and fled the countryside into the cities. Also the Bedouin tribes, Ismailis, and others in the hinterlands became clients to Muslim Amirs rather than Frankish lords and thus the balance of military manpower switched to Muslims with Crusaders relying on Knight Orders to hold strategic castles and the city guilds and some European pilgrims and very small retinues of important lords to hold the cities. This would be reflected in game by AOR units... if Crusaders lose hold of Edessa for example they would lose access to largest source of Turkomen mercenaries. Losing Aqaba means CS loses support of Bedouin Arabs, while losing Antioch and Tripoli loses AOR units of Syrian, Armenian, and Arabs.
On the other hand if CS gains Damascus it gains recruitment of more Arab, and some Ismaili units. Gaining Sis gives great recruitment boost to Armenian units, etc.
EDIT- I forgot one of the core differences in gameplay between mercenaries and other units... most mercenaries are able to be recruited in 1 turn vs 2-4 turns for other units since they are assumed to be fully trained and equipped. Paying for the mercenary barracks and controlling the additional unrest it causes will be the extra costs for access to such units rather than initial recruitment cost or upkeep per turn. Such AOR and mercenary units would be desirable then because they are more flexible than kingdom roster units which take time and planning to recruit. Mercenary barracks will be relatively limited availability- probably only in a few capitols initially and generally contain better units while AOR units tend to be local and rural light or medium units. However mercenary barracks and AOR units will have lower replenishment rates so very difficult to form the core of an army from only such units. Roster units will be needed because despite longer training time such units can be recruited and replenished anywhere the right level of building exists in faction control.