How would you guys go about relating State/Province with Cities, and how about Postal Codes too? I have three separate Taxonomies. Would you add Term Meta for each one to specify which term_taxonomy_id it relates to?

Or would I be better off with one hierarchical Taxonomy and just creating parent/child relationships?

I think post type admin screens are easier to modify than taxonomies but I would go with a WooCommerce Attributes approach and put the each "child" on a new page so you don't end up with a large list of hierarchical states, cities, and zips.

Well, I'm thinking more in terms of the "infrastructure". I like the idea of keeping each "entity" separate, and "relating" them with Term Meta. Rather than cramming it all into one space hierarchically. Just seems messy, even from a data point of view. At least if they're separated I can have custom Term Meta forms for each one a bit easier than if it were just one hierarchical Taxonomy.

and it may end up making the code easier to read and understand if they're separated.

Perhaps even simpler DB queries? idk