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 .

They both get a tremendous amount of blame for that (though Obama gets all the current blame), and I have a feeling the next President or two will continue to sweep the real economic issues under the rug -- nobody seems to want to make the hard decisions that involve purposefully keeping us in a recession for a long time in order to fix the underlying economic issues.Gotta run...have to get my nanny to turn off Fox News...don't want to be an accessory to funding terrorism!

See if you can find one with an already built, permitted, accessory apartment (in law) with its own entrance, sufficient parking etc...and I think just to defray the mortgage and learn about landlording it may work out.

And, what they will NOT finance is furniture and accessories...which is what the Seller is trying to get around by offering financing on the complete package.