It's almost 100% bo3 objects, and it's all underground! If you use proper block checks, appropriate dontPlace settings, and sequence objects correctly in the resource queue, you can spawn tons of things almost entirely seamlessly. For reference, here is the resource queue for this biome:
The biome is called TallForestCave and has really high vertical caverns and spawns within a parent ForestCave biome which has a completely different style of cave pockets around it resulting in what you see in the photos! I actually put thought into this!
I have been going places with cave experiments as of late and think I'm getting a firmer grasp on them every day (I have leveled up, as Pitman said). I might make an "advanced bo3 cave tutorial" one of these days if there is any interest in one.