Address concerns such as leaks and broken items.  

Look for someone who can present you per line item basis, and separate labor and materials, then buy materials.

Does item it's your only source of income?

@Marcia MaynardTwo items you included that are interesting to me, kitchen back splashes, and garbage disposals.

New roof, siding, central ac/heat, water heater, lights, carpets, toilets, counters and faucets (they are not gold btw) in bathrooms, paint, lots of new trim and finish items (vent registers, baseboards, etc.), and full clean up of yard and exterior.

Usually it will already have an inspection contingency that those items will fall under

Due to item 1, adding an ADU can require years to start achieving any return (once the accumulated cash flow recovers the initial negative position).4) ADUs detract from the existing structure whether this is privacy, a garage, or just yard space. 5) this is related to number 1, but there are many more buyers looking to purchase homes for their family than there are RE investors looking to purchase small unit count properties.

It is essential to be able to communicate very clearly and receive very itemized estimates for any work contracted out!

We are 6 months in and still have a huge list of warranty items they have yet to get to. 

Other items to look at include: hot water heater, plumbing, electrical, roof, siding, and the sub floor (look for soft spots).Hope that helps!