You have the mortgage, taxes, insurance, maintenance, capital expenditures (roof, flooring, etc.), and also need to consider the cost of vacancies or bad tenants.I also recommend you charge market rate, for yourself and the tenant.

Bought under assessed value, slight value add through cosmetic rehab (paint, light fixtures, flooring) What was the outcome?

You will get much further in your search by signing with somebody experienced in the space.

If you find a separate habitable space, the ADU cost is significantly less.  

For a more general philosophy on hospitality, especially if you are going into the higher end STR space I would recommend Four Seasons: The Story of a Business Philosophy by Isadore Sharp about the founding and development of the Four Seasons brand. 

In my early days of rehabbing I used to wonder how the heck do people miss-fire and pee all over bathroom floors.

Got this one for 30K, only needed floors and kitchen redone.

How do 5-7 people share food space, kitchenware, cooking time, etc?

We still need to calculate appliances, flooring, windows, HVAC, fixtures....My point is that we need to be putting away money to keep our properties in max market rent rate condition.

My experience says that the smaller the industrial space the greater the demand.