Please let de say that I'm a analog photographer without a lot of IT/exiftool knowledge.
I can provide my tif files with enough metadata, like camera, lens etc. But I was wondering is it possible to add:
Film brand
Developer brand
Developer time
Filmholder
...
In a way I can search these values in Lightroom, I think not but you never know.
Now I'm adding all of this in a small database.
There isn't a specific place for these tags. Your best bet would be to either include them in the Description or create a hierarchy and store it in HierarchicalSubject.