So I finally got the Khan of Khans achievement in the year 1443 (10 years before the game ends). It took me a little longer because I was very meticulous, and also didn't realise I needed to kick out all of the Holy Orders (including the Tengri one!) if they owned any land in the de jure Empires I needed.My advice to anyone also going for this achievement would be as follows:A. Aim for Medium Crown Laws after reforming the Faith and adopting Feudalism. It makes conquering Kingdoms with the Invasion Casus Belli far easier as you can simply revoke all of the infidel titles for free, rather than sieging down the top holding of every single province in that Kingdom (keep in mind you will still have to siege down the top holdings in provinces which are not a part of the de jure target kingdom of your invasion).B. Retinue is primarily for Faction relative strength. Mid-Late game it's just far too expensive to use and maintain in combat (unless you move your capital, which I didn't because I'm a Mongol boss), besides you will have more than enough vassal levies to throw around.C. Don't forget to take care of those pesky Holy Orders, and vassalise the Tengri Holy Order early on if you can (otherwise you will have to vassalise it later or expel it from your realm to get the achievement).D. Do not usurp Kingdom titles. It's better to create them yourself as the Kingdom will be created with the same Crown Laws as the Empire (only after you've adopted Feudalism and reformed the Faith). Thus any Kingdom titles you create will become Agnatic Ultimogeniture with Medium Crown Authority. It makes it super easy to create and manage the 'Four Kings' setup I had going (in the images below). Kingdom titles created BEFORE you adopt Feudalism and reform the faith will be Agnatic Elective, so try to minimise the Kingdom titles you create before the switchover (as you may need to revoke them if you want to create four Super-Khan vassals).E. Take the time to hand out titles manually to Tengri Mongols, don't be lazy. It really speeds up Faith and Culture conversion, which means smoother sailing later down the road.F. Don't be afraid to imprison and execute your 'average' son when you are close to death so you can inherit as the genius son that you've been educating yourself.G. Keep in mind there are some Kingdom titles you won't be able to create due to lacking the special creation conditions (i.e. the Kingdoms of Pisa, Venice, Jerusalem and Cyprus, among others). Thus, you will need to hand out the Duchies directly to the vassal that you want to own that land - you cannot transfer vassalage later. That is to say, if you want your King vassal to own the Duchy of Pisa, you have to grant it directly to him. You can't create a Duke and then transfer the Duke to the King as a vassal.That's all I can think of off the top of my head. Below are some images of my game map. There are four different map modes shown (in order): Independent Realms, Direct Vassals, Religion and Culture. Good luck!Independent Realms:The Four Kings:~West~~North~~South~~East~Religion:~West~~North~~South~~East~Culture:~West~~North~~South~~East~Cheers,-Caesar.P.S. Thanks to those on the forums that answered my questions regarding the Holy Orders.