Is there a standard average to look at (i.e. shoot for properties with less than 7 years to make down payment back)?  

The fee/increase in rent will cover the increase in water usage. 

The way I see it is if the property taxes are so high to keep from getting ahead with your rental it doesn't pay much to keep it or look at that area to buy.We had a inner city 6 plex,, our taxes jumped from 5400 a year to 6800 ... on a 6 unit building this was after we had contested the tax hike that's 133.00 per apt per year or 95.00 bucks a month just for taxes.per unit.. we contested the increase hired a appraiser had a meet and look at with the city appraiser.. it knocked it down for a while but went right back up a year later.. 

There are two times of cheap neighborhoods, the ones that are in the path of progress that will appreciate with time (Gentrify) and those that will just be cash cows and not increase in value. 

For value-add opportunities, go ahead and do them, and get the increased cash flow from it6.

It seems as if the rents are maxed out, and could not be increased much without owning all 20+ units on the street.  

If these numbers are in the ballpark, you have sufficient cash to buy 4 more similar properties, and increase your annual net income to ~$80K (that offers a lot more breathing room).Since you purchased your properties 2-3 years ago, I'm assuming you have very LOW rates on your notes; and therefore, I would not be in a rush to pay down these loans.

I agree with your premise but I suppose at this time that the opposite trend will take place - that the demand for city living will INCREASE, not plummet with self-driving cars.

That's our standard as well, and it is gross income. 

Area standard is What's left of the current roll and one full back up roll per bathroom.