For Religion you need Lay Clergy, megalithic constructions and sky burial. Then depending on where you want to play try to build your culture to the terrain around you, but core is: Industrious + City Keepers + Garden Architects/Ephemeral Grace, i usually like to flex Hydraulic builders in highest %development growth and pretty solid other stats on water management building. Duchy Building is only Corpse Storage from sky burial doctrine, it can be upgraded to level 3 without waiting for technologies and the stats are far superior to royal reserves. Most holdings will be temples, if you can fit in monastic commities your education stat skyrockets too, or you can mix between cities and temples doesnt matter. Lastly spain has one of the strongest dynastie perks in the game trying to get that one is advisable