[Taqwus]

The unit limit is total -- but I don't remember whether it's per side or for the entire world. Might be for the world; most nations aren't going to get close to that.

PD units are not actually real units for almost any purpose. You don't need to feed them, don't pay maintenance for them, can't assign formations, can't equip their leaders, their leaders are immune to assassination, they can't be affected by army-bLasting rituals, et al. I doubt they count against unit limits, because they wouldn't be stored in the unit table but instead as a statistic associated with the province which is only translated into units for battle.