Recently started a game with the Rus. Getting close to the time when the mongols come, and is not terrible teched up, can get dismounted Dvor from just recently captured Sofia only, but there are still turns left and I might get lucky (if I have understood everything correctly the Mongols may appear more or less everywhere on the eastern edge, so if they may not necessarily go after me, though I shouldn't count on that happening).

First I did was rushing towards Kiev, which I made my capital, taking Smolensk on the way. IMO Kiev is necessary, atleast if one has any interest of even the smallest amount of roleplaying (one part of my roleplaying is basing the faction leader in Kiev, while the heir is in Novgorod, so when I get new leader, he rides to Kiev while his heir rides to Novgorod), provides fairly nice income as well. Then mostly captured the remaining Rus cities (Ryazan and Moscow, Halich would go into this if it weren't held by the Polish) as well as Helsinki (mission), Caffa (nice potential trading port and only lightly defended) and Iasi (mission, starts as (poorly upgrade) castle and in good position to be Kievs first line of defense). Sent a diplomat and allied with Denmark, Poland and the Byzantines.

The only ally to backstab me was the Byzantines, they appearantly decided that despite amiable relations and the fact they already was fighting the Turks and Hungary (the Magyars however had failed to expand, so only the Turks where really any sort of problem, after the Byzantine backstab I accepted an alliance offer from their diplomat) they really wanted Iasi. They have refused peace this far, but recently I smashed one of their big armies and captured Sofia, so they may start to listen. Just before they backstabbed me I had sent armies towards Riga and Vilnius (both still rebel-held) who promptly fell. Sarkel and Bulgar are still rebels, though the Turks made one failed attempt to assault Sarkel (the entire Turkish army involved was wiped out).

What I have noticed about the Rus.
One thing towers on the border is a good idea, so when/if the Poles or other come, you can actually have enough time to prepare and gather your forces, your settlements are so far away from eachother that one really needs more time then many other factions. The idea I have, is basing a bunch of cavalry in my castles, ready to rush towards any city that is threatened, while all infantry is to be provided locally. Due to the peaceful Poles in my game it hasn't really been tested.

Another thing, while they have some decent infantry, it isn't that easilly available, it takes lot of time even to get the standard spearmen (the castle types, I haven't had time to use any, recently got able to train them in Smolensk and can train them in recently captured Sofia but that's it), on the plus side ones cities provides archers very quickly. As far as cavalry goes, Kazaks are good dependable horse archer that should avoid hth combat. Boyar Sons are competent medium cavalry, one should use their javelins to their full advantage before going to hth. Druzhina is the first heavy cavalry one get, not that bad, but very vulnerable if bogged down.

And as far as economy goes, not that good, but it is manageable.

And when it comes to capital i can see two choices to begin with, Novgorod or Kiev. The difference is mostly where one wants to have ones focus. Regardless of which one chooses Poland will always be a reasonable area to expand when the oppurtunity arises, but other then that;

Novgorod: If one wants to focus on the baltics, conquer Scandinavia and generally fight in the northern part of Europe. Good thing, not that many threats to your horse archers here, but there are problems for your armies, like Polish Nobles to name one, but they may always be a problem. Bad thing, will have to fight catholics and only catholics, Pope may become antagonistic, and crusades against you may happen if youre unlucky.

Kiev: For the southern route. Bad thing first here, those you will mostly fight, Byzantines, Hungarians and Turks, all have horse archers of their own. Good thing, only Hungarians (and the ever existing foe, the Poles) are catholic, so Pope may not potentially become as hostile, but do not count on it. Possibly greater wealth around here, but I'm not experienced enough to really judge that.