Playing Poland right now on M/M. These are just some random thoughts about things that worked for me, not a strategy per say. First 3 things I did was blitz Kiev and get ports in both the Baltic and Black seas. Got a marriage alliance with the HRE and an alliance with Hungary. The lousy infantry was a bit of a problem since walls are a pretty effective counter to mounted troops. Merc spearmen and Slavic mercs are pretty effective though and peasants can drag a battering ram just as well as anyone so walls weren’t a huge issue.

I captured a few of the small settlements to the east partially to nip any Russian expansion in the bud but also to beat up on some non Catholics and make the pope happy. My diplomat by Rome is mostly there as insurance, conquests alone maxed out my reputation with the pope.

It's important not to take too many of the piddly little settlements to the east. It takes too long to build them up and they are just money sinks until you get the rest of your economy going. I'm going to have to start taking a bunch of them soon though just so I can have some speedbumps in place when the Mongols show up though.

First crusade was called at around 1105, I shipped my best general out through the black sea and made a beeline for Antioch. Managed to finish the crusade in 4 turns.

By this point I had to turtle. My economy couldn't take any more expansion. I slashed my army sizes to manageable levels and focused on building up my cities. My next big goal is to get Constantinople and possibly convince the Pope to declare a crusade against the Russians. Beyond that I'm not sure. I'm debating war against the Hungarians. The pope doesn't care for them, while I have 3 cardinals and maxed reputation so I'm thinking I can mop the floor with them without having to worry too much about my reputation.