I just wasn't entirely sure how much I could store in the files, and how to properly handle it. I think I have it figured out though with a little testing. Was trying to save myself some time. I also wanted to prevent it from saving settings on a specific character for specific stuff to prevent issues. Not sure how that is done either.
I don't use them much, but IIRC the <global> node contains the default settings, and <character> nodes contain specifics that overload the <global> ones.
I don't know if there's a strict limit - probably not worth even concerning yourself with it until you see lag/choppiness due to memory usage, and even then there's functionality to check what memory usage each addon has.