Taking most (pagan) rebels around Vilnius will give you a base from which you can launch attacks and defend yourself, if needed be. Riga, Palagna, Hrodna and Mensk are the most logical settlements, but Reval is also good to take. I don't recommend going further west for now, as Poland will most likely try to take those settlements, whether they belong to rebels or to you. And I don't think it is a good move to get into a war with Poland early on. You'll have to fight for every step you make into their lands, and their lands are rather poor, not really worth the battles you'll have to fight. Rather, try to form an alliance with Poland, so you can concentrate on your eastern problems first.
In the east lie to rich settlements: Novgorod and Kiev. However, they are the core lands of the Republick of Novgorod and the Grand Principality of Kiev, respectively. Going to war with these factions is inevitable, even if you do not fight them, they will fight you. However, getting into a war immediately isn't a good option either. Together, they might be able to keep you in check and even take one or two settlements. On top of that, Kiev isn't developed yet. So the best option is to attack Novgorod, and defeat them in a quick war, to prevent Kiev from joining the fun and killing valuable soldiers. If you have secured your new lands, your economy should be good enough to have several armies around to take Kiev down.
I for my self wouldn't go into Russia further than necessary. It takes ages to move your armies around and the land is rather poor, not worth taking. After you took Kiev and a few surrounding settlements, make peace with them. They will be finished by the Cumans. If not, you can always return later on.
Now, with your eastern border secured, you can look westward and southward. Buy any settlements your victory conditions demand and then march south, to take Hungary. If you are taking over Hungary, better ensure you have good relations with the Romans, otherwise you have the risk of facing both the powerfull Roman army and a crusade at the same time. After Hungary has fallen, try to obtain a port in the Adriatic sea, if you don't have one already. Use this port to launch your attack on Rome and the rest of Italy.
Now, with Italy, Hungary, parts of Russia and all of Lithuania answering to one mighty pagan king, who could possible stop you?