You need to shrink the ARV range to 5k or less. 

Dan,A typical property management fee could range anywhere from 4-10% of gross rents (larger properties get the better rates due to the economy of scale) in addition to a per door bookkeeping fee, let's say $5/door.

I am looking for a condo in 150-180K range for my elderly parents (Phoenix metro, East Valley).

I would suggest being present when this happens so you can see any issues yourselfGet copies of current lease, operating statements for 2 years, any appliance/HVAC/Water Heater purchase receipts, utility bill copies from the sellerDecide what you're going to do for property management.

My calculations indicates a hot water heater has a cap expense of $12/month. 

Also, on the 2nd photo (see photo below), there are some sort of "meter" connecting to the hot water pipes.

It’s an already roughed out half bath that needs a toilet, sink, mirror, plus the valves for H/C water under the sink and the water valve for the toilet fill.

We own several duplexes where the water isn’t separately metered.

I've been looking at past comps and comparable houses being sold are in the same price range as what we would price ours at.

We achieve virtually 100% occupancy from $91 (think early Nov mid week) to $471 (think July 4 weekend) per night per each unit (so Property rent ranges from ~$200 to over $900 per night).