Btw hey link! I think you remember me from the old days on the aoe discord , im from spain and your concept is actually good .
But here is what i could add.
Starting off spain would be a civilization on its own , wich will include the kingdom of asturias , leon , castille , aragon and finally late imperial what we could call “spain”.
Dark age : selected kingdom : asturias. Spain can age up ONLY with the tc , but they still can build their landmarks , but the dont provide any age up bonus . every age has a landmark . so only 4 landmarks for spain . If they age up with the tc they can change their “kingdom” with their dark age “landmark” , so then you would have leon!
Asturias kingdom provides : Access of the early reconquista bonus , every battle you win (at least more than 10 soldiers) to be considered battle gives you 100 of each material . Scouts also can use pikes instead of swords or bows , but they are much slower.
Feudal age : you have access to the spanish mill , it works like a mill on aoe3 , infinite food and you can add multiple villagers to it . The technologies here are much slower to be researched but the time it takes to gather food is faster.
You have access to the horseman , archer and some pikes.
Leon kingdom provides : mid reconquista bonus : every building of an enemy destroyed gives you 50 of each resource but your troops are faster .
Castle age : you have access to the knight , the archer , early arcabuz (handcanonner but with lower damage and health and lower attack speed but much more faster) , and you have access to the inquisitors , they heal as twice the speed and they cost more . You also have access to the hacienda , wich lets you train some tax collectors but you cannot inspire buildings to boorst their training time neither multiply gather rates.
In castle age you can select now from two kingdoms , instead of being forced to only one kingdom at each age .
Kingdom of Castille : spanish keeps are abviable as its own , cheaper keeps , low health , defense buildings are cheaper and it unlocks an special building that acts as a troop trainer but you have to look for gold to make 2 units in the time of one . like the mongol ovoo . It also lets you upgrade to “early tercios” wich are spearmans but they are OP .
Kingdom of Aragon : It lets you every naval boat and every naval upgrade to be free for a limited time , then you have to wait to aply the same boost or advance to the imperial age to use the bonus again and change to the kingdom of spain . wood rates and food rates are increased by 30% and gold looses its importance , since every unit in game cost only wood and food , but their cost its highly higher .
It also lets you aply for the late reconquista bonus
late reconquista bonus : every unit you kill will be a free unit you can make of the same type + every enemy unit you kill gives you a bit of everything (resources)
Imperial age : You have access to the university , tercios recruiment building and the Late hacienda .
The late hacienda lets you transtion from the old haciendas to this new building wich lets you gather every resource in game but in a more slower pace , works like the aoe3 mexican/spanish hacienda . They cannot make soldiers tho in the hacienda.
The tercios recruiment building lets you make 4 tercios pikeman at the same time BUT you have to expend as many resources it would take as normal . But its worth the cost.
Spain kingdoms offer : Tercios upgrade , it unlocks their special unit (early tercios are just an upgrade of spearman) but Tercios are a unit on its own , able to pick from melee atack with swords , change to early arcabuces , or be spearmans on its own . with specials abilities and more!
It also unlocks arcabuces and bonuses at mining the furthest gold you have from your TC .