Besides being careful about country, currency, and hierarchical structure planning, scripts, workflows, templates, fields, formulas, searches, datasets and workbooks referencing subsidiaries, what are some things to watch out for when creating a new Subsidiary?

Nexus, locations...are two off the top of my head

Yeah I'd say locations. If there's even a 1% chance in the future you think you might have inventoried items, do not associate a Location with multiple subsidiaries. If you then ever try to use inventory functionality, it becomes a nightmare

Taxes Intercompany Accounts/Processes Allocation schedules Chart of Accounts Items

Thank you everyone! @Jay Flynn09 @RJMNS @MGBC