How to create a primary normal(or displacement)map and a secondary tertiary map?

Not sure where to post this, but it’s related to shaders so I’m trying here.

I’m creating a character and I’ve been thinking about how to have one normal map for the primary shapes and then a tertiary normal map for skin details such as pores and finer wrinkles.
The primary shapes normal map should be baked for each character whereas the tertiary is added as an overlay in the shader. That way I don’t have to do heavy sculpting and projecting in ZBrush and bake it down explicitly for each character.
Only the primary shapes are baked down and and then combined with skin details in the shader.

The idea is that I might settle with normal maps, but this process could also be used for displacement if I want to go for higher quality.
So I could have the primary shapes as displacement and then the finer details as a normal map, basically the same map as for my lowpoly, only 16K instead of 4k or 8K, instead of going displacement full on. Maybe there’s no advantages of using normal maps if I’m going for pre-rendered images? Just use displacement maps?

Either way. I’m looking to split up the primary shapes from the tertiary shapes and was hoping someone have some really great tips.

What I’ve done is to smooth out the highest subdiv in Zbrush and created a normal map from lowest to highest to get a smooth map, following the characters body shapes, muscles.
Then I did a normal map from level 3 to level 6 with all the sharp details to get the finer tertiary shapes.

But I’m thinking. Could I bake out a normal map of the full range, level 1 to level 6 and subtract the primary normal map from this full range one to like “flatten out” out so there are no larger shapes in the map, only the tertiary details?

For a workflow point of view I think it would make more sense to work with displacement maps and have Mari as a step in the pipeline. You’d bring in the maps and decide what to use them as. Will they be painted further, or just baked out to normal maps. This of course depends whether I would get the same results from baking Displacement to normals in Mari as I would in XNormal.

What’s your guys opinions and thoughts?