"Keep your friends close but your enemies closer." -- Michael Corleone
I think this game is ripe for a cultural victory. You have almost all the turf you need; future cities have already been pointed out for you.
There is no good current target for war. Mehmed would be the best but assaulting him would draw the ire of both Ragnar and Toku, which is no good.
I would try to spread buddhism to all of Toku's cities quickly, Ragnar's cities will probably follow suit on their own, but I wouldn't make Rangar's lands a priority. If Mehmed founds a religion and converts (and we should hope he does), it will be an excuse to gain Istanbul and the Marble city.
If you could get Toku as an ally, later on if things get tense with Ragnar, you can probably bribe Toku to war against him.
Focusing on border culture is key, drama, music, running artists, religious buildings. Is it still possible for you to found another religion? A GS for philosophy en route to liberalism would be good. Founding other religions won't affect Toku and Ragnar because they'll be running theocracy so they won't spread.
For military, X-bows with shock will be clutch. Throw in some barrage catapults, and pikes to deal with the cavalry the AI seems to favor. You'll need the required archer for each cities defense but defending your homeland is all about reduced pillaging.
Optics is also a key technology. You need to get over there for trading and to stir the pot diplomatically. It just needs to be hoped different civs have founded different religions. If Victoria is over there, she's a target. Man, does she tech fast in patched warlords. Anyway, if you can keep the other continent at war with itself, it will hold them back. Later on, you can bribe the Toku-monster to attack whoever is in the lead. Aggresive + Protective = bad news.
So that's it. Just follow these simple steps and the game is over, right? Nothing unexpected ever comes from this game.
If this plan gains acceptance, more can be discussed on the execution of securing a cultural victory (the whats and wheres). If not, I'll be happy to watch the war engine rev, especially when fighting Toku.