I prefer good service over saving 20 bucks a month.

When the time comes will use online services to market the units.

When I realized what happened, I called customer service and humbly inquired about whether they would be willing to extend the 0% interest promotion once more given my stellar payment history with the bank.

Typical service call is 60Bucks for me.

During your due diligence you'll want to back up the financials with one year's utility bills, copies of the service contracts, and a lease-file audit (comparing the leases to the rent roll).  

There are plenty of services you can subscribe to to get even better data than the MLS because they give you all sales, not just sales through the MLS. 

A good goal would be to work up to 6 to 9 months of debt service in reserves. 

What kind of due diligence services do you provide?

I can recommend my guys all day long, but if your deal is in an area where they don't or won't service, there's no reason to make the recommendation. 

I would take a slightly lower return for a more passive investment.  3) the amount of riskI could take the money you would use to pay down your mortgage and place it in something very passive and somewhat low risk such as the S&P 500 long term (14 years is long term) and achieve far greater return (historically probably double) than what you will save by paying down a conventional home loan.