Give a Dog a Bone

Character-locked: Matilda di Canossa, 1066, with three boxes to tick. Italy: fabricate claims on the independent Italian counties (restart if your Realm Priest has poor Learning - he's your claim engine), and get the Duchy of Lombardy claim by befriending or hooking the Pope; that's enough to form the Kingdom of Italy. The 50 dynasty members are the long pole: land every son and matrilineal son-in-law you can - rulers and their spouses get a fertility bonus. The Holy Order is the easy bit once piety allows (Non Nobis Domine pops if you haven't got it). A proper single-run project, but very doable in Matilda's lifetime plus a bit.