Muffler shops, car washes, Fire work stands, Insurance offices, Medical plazas, daycare buildings, etc. 

She does easy chores like wiping off surfaces, putting laundry away, and I supervise her vacuuming.  

I've read quite a few Q&A's here that basically say, "as long as 75% of the rental income will cover the mortgage then it's essentially a 'wash' and should not increase your DTI." 

Interested in possibly adding addition by turning garage into extra bedrooms and connecting to main house with "shared laundry room". 

Try washing them and use a Mr Clean eraser to see if that takes the marks off. 

The ones that don't pay online will either put cash in the bank or drop a check in the slot for my onsite guy to deposit with the laundry coin and his rent.I'm going to look into apts.com and see if that may be a better solution.

anyone have personal experience or advice regarding owning a laundry mat business AND building.  

Buy a house now, maybe it isn't the nicest but needs some light repairs, maybe a new coat of paint, maybe power wash the siding.

We are researching the multifamily laundry services for 16 units building in Chicago area. 

ADUs often have the separation you're describing.Most homes in the areas you listed will have shared kitchens, shared laundry, etc.