What's the layout of the room? 

If you don't change the layout, you can have tubs resprayed professionally.

It will require complete renovation including down to the studs, reconfiguring the layout and adding a third-floor loft-style apartment.

The layout of the condo is strange where the hotwater heater is located in the garage (which is deeded to another unit(unit 3)) and the water and HVAC system are located in a utility closet in another unit(unit 1).

In my BRRRR projects I tear out the kitchen and improve the layout, all stainless steel appliances, (the cost is minor compared to white appliances but looks so much better) open up walls for the open concept, gut the bath minus the tub (refinish the tub), new flooring (mostly hard woods), replace windows if necessary, new six panel doors, paint the entire house inside, possibly paint the outside if necessary.  

The general character, look and feel, etc. will most likely remain low-income for the immediate future just due to the architecture, layout and demographics. $350k is a decent price for a duplex anywhere in Boulder County, it’s a very entry-level price point.

Parcel layout can also be bad and not have enough parking spaces for the business model.I understand why you want to get passive.

I think the the detached ADU that will be under 750 sq ft. is not the main concern on this property since the ~430 sqft layout that is currently there is already permitted and I just want to add on to that. 

Also, does the layout of property make sense to change into multi family.Podcast: https://www.biggerpockets.com/podcastWebinars: https://www.biggerpockets.com/webinars

You will need to follow their regulations and have a drawing for your layout plan.