According to HUD guidelines, they should provide you a letter from a healthcare professional, licensed in your state, indicating the need for an ESA, and mentioning an ongoing relationship.  

I was served a certified letter by one of the six tenants at a student rental house stating my lease was void because of violating  Wis.

Make sure to research local rates for cohosting and management services to stay competitive.If you're doing this as a side gig or part-time job, it’s essential to time block, create systems, set expectations with property owners, and establish boundaries to ensure a smooth experience for everyone involved.We opted not to pursue rental arbitrage for two key reasons: dealing with landlords and the significant upfront costs to set up and run a profitable STR without the benefit of property ownership.

Block.

Depending on the construction of the building (block or stick, etc), you will want to test the connection strength.  

There are two distinctly different collection strategies you can pursue:1) Collections Company: there are several that ALL they do is pester the debtor for payment with calls, texts, emails, letters, etc.2) Collections Attorneys: they will get a money judgment for balance owed and then pursue garnishment as necessary - including garnishing any state tax refund (if the state allows).Both will take a percentage of what they collect.

Do you recommend doing a lease termination letter, just to have something in writing?

Know your numbers, strategy, and block out the noise. 

Would this be a letter of intent or promissory note?

We found our forever home in the neighborhood we wanted by driving the entire neighborhood, adding the properties using DealMachine, and then sent them all handwritten greeting card letters stating that we're a new family looking to move into the neighborhood and if they had any interest in selling to please call us.