It's quite possible to take most of Europe before the Holy War CB runs out, at which point you're pretty much unstoppable.
Am I the only one who found Ottomans really easy? in my current Ottomans game at ~1480, with NO reloading, my empire spans from ersukjavar to azerbaijan, I have all of egypt (to cyrenaica) and all of Arabia (Yemen, Jalayirids, Oman and Hedjaz, najd and al haasa don't exist) under PUs, so when my current king dies I will inherit, with cores, all of that + East Africa. Tripoli is my vassal, as is a shrunken Adal, Portugal and Spain I have beaten to a bloody pulp and I always beat the Austrians (HRE) When they declare war on me every five years. I always attacked, never once used scorched earth, and my fleet is second to none but England's. I control all of the aquilean lands, all of Greece and all of Venice's starting territories, including the COT. I have colonized Astrakhan.
For people who might say I was given no challenges, I had to fight to gain all of those PUs, fight off the timurids (now my eastern border dominated by a lsrge and sunni ally called Persia) and around 1430 I was at war with France, Austria, Bohemia, Burgundy and Castille all at once, and won. playing on normal with regular settings. I'll post pics later if I can find an imagehost I like.