Does anyone know of any people who have successfully navigated building an ADU on their property locally? 

I live in NJ, and it has a very high cost of living and with the current rate of interest, makes it a very pricey market so to say, and not that investment real estate friendly.

Super Jumbo mortgage loans and lenders can vary widely in their rates and qualifications. 

What you choose to do won't make or break your success, how you choose to do it will.

I keep wondering about insurance, vacancy rates, if tenant selection is a bigger/ different factor, terms of the tenancy and differences in opex and capex? 

I ended up turning back into an ltr, since it wasn't successful as an str at that time. 

That's true of every market now, I suppose, with interest rates and supply problems, until either prices go down or rents go up.

Its easier to have investment success in areas with growth, as a rising economy raises all values. 

Right now the mortgage rates I'm being quoted for a 20% down DSCR is 7.75%. 

Cooper) said that the mortgage is assumable (there is path that would allow me to remove spouse from mortgage and retain the current rate), but the process can take a while, is subject to fees, and they need to reevaluate my ability to qualify for the mortgage without my spouse.