How to set up lease and mailing address on accessory dwelling unit?

[JT Spangler]

I'm currently in the process of purchasing a 2/2 cottage with a 1/1 basement apartment (that needs quite a bit of work, but it permitted). I'm wondering what the process is to get a separate lease signed for the ADU, and to get a separate mailing address for it -- is this even possible? Basically, where to start? County records, inspector, USPS?

Property is in Nashville, TN.

Thanks, BP nation!