My ironman Zemgale playthrough is going okay. I managed to form the Kingdom of Lithuania (and get all its de jure counties save one, which is next on my list), although I've gone a little bit North Korea and I'm holding a desmesne of 11 out of a maximum of 6.
I've got eight(!) children, four of whom are male. Gavelkind succession is going to be a bitch. I'm trying to arrange it so that my heir is due to inherit two duchy titles and all the counties under them (ideally), but it's proving tricky to do, as the game won't let me simply
give him those by choice. Obviously this is to stop me gaming the system.
However, it
does apparently still allow him to
demand territory that he desires. I managed to give him one of the duchy titles that way, after granting him one of the counties within it.
Still, dividing up the territory is going to be painful, particularly with the short reign modifier after my first king dies. I'm holding four of the five Romuva holy sites, so I'm tempted to make a push for the fifth and reformation before I die, hoping that I'll have enough swing to change the succession law immediately upon reforming (to primogeniture, I guess). It'll be tricky, though - the fifth site is a fair distance away, I have no casus belli, and the ruler has multiple allies. Hrm.