Thanks for the comments guys
@Gimhad - Immersive Interiors doesn't need to be bashed anyways
All Natural has an optional esp to be imported into a patch but that's only if something edits cell data after All Natural, it's not required and won't mess things up.
Also with the NPC thing, what I did was create a guard type character (that wasn't actually in the guard class so he couldn't just run up and arrest you). Two of these went on two different patrol style routes around the exterior of the interior cell, and the actual interior was placed in a subspace so they didn't get confused. It's something I'll definitely look into further for busier areas, but it'll be pushed to last place in terms of importance and will be entirely optional if it ever happens.