After Overlord season 3 ended I started reading the light novels so if they can match what has been happening I feel like we are in for a feast of the eyes. This is going to be one epic season!
As Season 4 is only adapting two light novel volumes, as opposed to three in each of the previous seasons, I hope the writers will also adapt some of Maruyama's side stories, e.g., the Ainz Ooal Gown guild members' conquest of the tomb that will become their guild base.
If they are only doing 2 novel to adapt it would have to be the sacred kingdom arc. either that or their going to do the dwarven thing and the first part of sacred kingdom. But I feel like Vol. 10 isn't really a need to adapt volume.