I live in Murray and they now allow legal ADU (Accessory Dwelling Unit) aka basement apartments.  

What you are wanting to build is an Accessory Dwelling Unit or Junior Dwelling Unit, which hopefully your zoning will allow.

As far as packing an accessory dwelling into your home and vacation renting. 

The other option is to build an addition with an ADU (accessory dwelling unit) finishing the house and adding another 650 sqft to the main house ( 3 bed 2 bath ) and a 550 sqft attached ADU (1 bed 1 bath). we could rent the ADU for appx $1000, to $1200 a month.

In the Utah market, the distinction lies in "owner occupied accessory apartment" vs "legal duplex."  

Put shelving in the showers to hold shampoos, soaps and razors(Command) makes great shelving for these accessories(Command Shower Water-Resistant, Clear Frosted, 1 Caddy, 4 Strips (BATH11-ES), 4.8 x 11.3 x 6", https://www.amazon.com/dp/B00H... ), makeup mirrors. supply in the kitchen anything that you would use in your own home. 

Hope this helps.Core and shell means not including any finishes, like cabinets, bathroom accessories, wood flooring, etc.

The City of Vancouver is very ADU friendly: Code stuff -- https://vancouver.municipal.codes/VMC/20.800 and an overview --  https://www.cityofvancouver.us/ced/page/accessory-dwelling-unitsGood luck!

It sounds as if you may be able to include in the scope of work renovations to have the property conform to a single family use or a single family with accessory unit use.

Then what happends is anyone reading your post might become an accessory to a crime whether you go through with it or not .