If you go down the FHA/HUD road, please learn in advance about the annual auditing requirements, 1-3 year recurring REAC inspections, 1-3 year recurring Management and Occupancy Reviews, etc that will be imposed on you.  

I do this so often that I created an online tool which enables me to instantly estimate a break-even price (where rent equals recurring expenses).

That's a recurring theme in your responses.  

And, the total of your mortgage payments, plus any other recurring monthly debt (credit cards, car loans, student loans, etc.), can't be more than 43% of your gross monthly income.So, assuming you have no other debt at the time, you would only qualify for an all in mortgage payment of $465/mo.You're credit isn't going to be a problem. 

Assuming you could find a firm willing to separate out the pm Side of their business, must be over 500 units, does anyone have an industry standard multiplier for the recurring revenue/profits of a well run PM Business?

The tenant can set up a recurring payment if he wishes, or he can do it one month at a time.  

I do this so often that I created an online tool which enables me to instantly estimate a break-even price (where rent equals recurring expenses).

www.erentpayment.com will do that, if you set it up as a recurring payment.

v=LGZkALqw2NQSummary : There are pro/cons of being  agent just for MLS listing.There are yearly recurring charges of being agent.

To do this, they would just set-up one-time payments instead of automatic, recurring payments.Just as a note, tenants can either login and set-up their payments each time, or they can set them up as far in advance as they'd like, depending on what they're more comfortable with.