But after considering these other factors (bathrooms, hallways,  ADA compliance), I am concerned that I'm unable to provide what they are asking. 

Department of Justice's publication Frequently Asked Questions about Service Animals and the ADA which are relevant to your situation:Q: Are service-animals-in-training considered service animals under the ADA?

John, I am not a licensed pro but I will share with you some of my thoughts as I'm AD as well and have been through this process a few times.  

Hi.....I seek homes for folks that are wheelchair/ADA/Disability set ups.  

If they have not confirmed an hour prior to their appointment, I send this text to their phone (which was required as part of their contact information I required in the response to my ad):As I had requested in my email, you have not yet confirmed your apartment showing for this evening, scheduled for 7:00pm.

ADA clearly indicates that it must have specialized training and that cats do not qualify. 

The toilet must be ada height, light switches and bath mirror must be a certain height.

Emotional support dogs are not recognised by the ADA as a service dog.

Its reflected in Dodd-Frank, ADA, Fair Housing, local eviction laws, Etc - all of these came about because of a small group of people abused others to such an extreme level that the gov't swoops in and decides protections are needed and they go to the opposite extreme in their policies.

Actually the market for ADA accessible housing was my first thought but I didn't realize there was a large enough market.