I’m on the central coast and have one STR in a college town that grossed over $10,000 this month. 

If the other houses you own have no loans could you stack all their combined monthly rental income to pay off the remaining $120k mortgage before you retire? 

Monthly rent in the ~$1.5/sqft range.

I have (13 months) remaining on a lease of a townhouse I am currently renting.

The only thing you should be aware of is there is a section 8 specific inspection prior to move in that usually takes 1 month to complete so best case scenario is usually a section 8 tenant moves in in 2 months often its closer to 3 months if you fail the inspection and have to be reinspected which is common.

I am looking at Indy and Cini, OHI know it's been 8 months but now I am filtering the forums and narrowing down to "multifamily" + "detroit" that I found this post!

Here is the specific language from Assembly Bill No. 68:a local agency, special district, or water corporation shall not require the applicant to install a new or separate utility connection directly between the accessory dwelling unit and the utility or impose a related connection fee or capacity charge, unless the accessory dwelling unit was constructed with a new single-family home.If the Planning Department is telling you that you need separate utilities and you're adding an ADU to a lot with an existing SFR, refer them to the above language from AB 68.

Some loans may have seasoning requirements for the down payment money like you see on conventional loans for primary residences where they need to know where that money was the past couple months.

With that said, I work with Elizabeth Louis: https://elizabethlouis.com/I signed up for a 3-month coaching program for $1,500 per month to give you an idea of the costs.

Couple hundred bucks a door monthly cash flow, double digit ROI, and yes the prices appreciate and you build equity.