Mailing/emailing a notice to "start the clock" doesn't cost much and should be done to NOT lose time if tenant doesn't pay.

Do you feel like it has enhanced the productivity of your assistants to a magnitude that's worth the cost?

When a PM does charge a markup, he's usually getting a discount on the service to keep the cost stable.

@James Boreno You’ll likely owe taxes, but don’t forget to account for your adjusted cost basis, which factors in the original purchase price, depreciation over 10 years, and any capital improvements.

In the desert it costs me LESS than $20 for water.

A lot of it depends on when & where you're investing and how good you are at each one of these.

Right now your loan is costing you around $6000 per year. 

It can depend on the property, but owner paying the bills seems rare these days. 

If you are going to do a HELOC then you must understand the cost of using those funds.  

You would end up saving the higher interest rate on the HELOC as well as closing costs.