Best Succession Law for Expanding

I like Elective Feudal since it allows to hold multiple kingdom titles at once without any opinion malus.

You don't get an opinion malus for holding multiple kingdoms in any succession, that only happens with duchies. If it's not your main kingdom were your capital is though, de jure vassals of that kingdom will have a negative opinion.

It also enables to hold multiple kingdoms without being an emperor.

You can do that with any succession?

Is there any reason to favor another succession law if playing for expansion?

Primogeniture is always the safest, just like CK2.

Does it make sense for an emperor title character to hold multiple kingdom titles at once?

No. There's no real benefits and it prevents de jure drift of your main kingdom and pisses off the de jure vassals of any extra kingdoms you have. At the same time, when you create a kingdom after getting 51% of it's de jure area, you get de jure claims on the rest of the kingdom, so you can't pass up the opportunity to go ahead and create it.

/r/CrusaderKings Thread