However, if you put it as a primary residence house, the only liability you will be counted towards is the monthly mortgage payment of the house and removing your rent expenses (since you moved out).

My area (Seattle area) is clearly very expensive.

The lesson learned here was to meticulously calculate all expenses, including those often overlooked.

If you don't want to go to the expense of a security system, they have fake cameras with flashing lights that you can mount around entrances.

I think 160k for 500 square feet ADU is way too much I think, But it also depends on what city you want to build contractors tend to charge more on high end expensive cities. 

The price of the property, and what the bank will finance, will be based on the income the property produces, the Net Operating Income (Gross revenue minus expenses) divided my the Cap rate.

In our markets we pitch the floorplan we have and build cost and then help identify lots that can be built around and analyze the submarkets to see where the investors and us both agree to be the best fit for their strategy (hold or sell for a profit since we build about $155 a sq ft with margin and homes sell for $219 per sq ft on average) and based on that we build it on their construction loan.

We like the less expensive/rural areas as they seem to generate higher RoRs.If you're looking to network locally, there is a great REIA meet up in Matthews, NC I attend weekly and would highly recommend.

We don't need the cash flow, but it would be nice for building a reserve for repairs, covering expenses in slow months, etc. or for our next STR purchase!

Lease dates, income, expenses?