https://stadiamaps.com/terms-of-service/
> permanently storing results for future use (e.g., as a database column), in part or in whole, from the Stadia Maps Geocoding APIs without an active Standard, Professional, or Enterprise subscription with appropriate permissions;
Thanks - that quote is from a list under the heading "Furthermore, you herein agree not to make use of Stadia Maps, Inc.’s Services in any of the following ways:"
(Having scanned those terms I'm still not 100% certain I can confidently answer all three of my questions though. A classic challenge with this is that terms often have language that relates to map tile images, but it's hard to derive if those same terms apply to geocoded lat/lon points.)