Defending Russia from multiple crusades is a very real possibility. Being a Christian faction will not protect you from the whims of the papacy as orthodox Christians are seen in the same light as pagans, muslims & other heretics.
While Russia is not well endowed with quality infantry units (especially in the early stages), the Russian cavalry is of excellent quality, perhaps even the best cavalry roster available in the game. The Russians have huge distances between the cities to cope with but this can be as much of a blessing as a curse as their enemies also have to deal with these distances. It was no different in medieval times when Christian Crusades and Mongol invasions had to be dealt with. The Russians have a history of absorbing foreign invaders within the vastness of their country.
