What are some staple unit compositions that the Slavs can go for in the Castle & Imperial age?

I'm a new player learning the game. Been mostly playing Mayans, but wanted a second civ to switch things up. The Slavs seem like a good choice because while they have weak archers, they have a flexible eco bonus in the lategame, and seem to have quality siege and flexible cavalry and infantry.

But I'm struggling a bit figuring out what are some "starter" unit compositions I should aim for. I've tried a mix of Halbs and Onagers, but it was a bit lacking (particularly given that microing the Onagers properly is hard), and sometimes I'll just transition into a mix of infantry. Is massing Boyars reasonable? (or are Cavaliers preferable). If I save up enough resources for the unique tech (infantry aoe), are mass Halb/Champion lines viable? If their siege is good, what goes well with that?

Any advice for some castle, early imperial, and late imperial unit compositions that hold up well? Obviously these will have to be adjusted based on what you face, but for a new player I just need some things to aim for.