You are handicapping yourself by doing the single family first. 

Trenching, utility connection charges and etc. add a huge cost handicap which makes the economics unworkable in almost every case. 

One booking 6 weeks from now really handicaps your ability to book MTR guests. 

I will be dealing with adults, not handicapped individuals.

I dont think Don or Chris particularly are hurt with this as they have long standing and loyal client bases and it wont affect me personally either but it sure does handicap others wanting to get started who may not have the long successful track record .

Also we plan to have the ADUs handicap/wheelchair accessible on the first floor.

They would need to make "improvements" to the property, wheel chair ramp, handicap accessible showers, etc.

She likely can turn to legal assistance for tenants rights, especially if she’s taking care of a handicapped son, so be prepared for resistance.

Most “service dogs” are not service dogs, just like most folks parking in designated handicap parking places are not legitimately handicapped.  

It shall be an unlawful discriminatory housing practice for any person, or any agent or employee of such person:To refuse to consider as a valid source of income any public assistance, alimony, or child support, awarded by a court, when that source can be verified as to its amount, length of time received, regularity, or receipt because of race, color, religion, gender, national origin, age, familial status, or handicap;"https://www.ok.gov/OREC/documents/CompleteDiscrimI...It is illegal in Oklahoma to discriminate against an applicant because their income is from public assistance.