Your best bet is to find property owners that are interested in selling, but haven't contacted an agent or actually posted it for sale.

Best bet is to find yourself a realtor who has access to the MLS.

I would ad that once you clear you debt and have some free and clear property I bet is will not be hard to get a credit line based on the free and clear property.

I think your best bet is to leave it on the market and see if you can find a buyer in the slow time.  

Who is your primary tenant population: students, workers at a local institution or factory, retail workers, working poor, etc.?  

This is one lesson that I'll bet that you don't forget.

His property is poorly advertised with an ad on craigslist that doesn't even pop up if searching for multifamily.

I've been a software developer for 17 years specializing in Microsoft technologies and have my BS degree in Information Systems.  15 years ago I started learning about RE investing from a co worker that was embarking on this journey, and I read books like Rich Dad Poor Dad, Cashflow Quandrant, Total Money Makeover, How to Win Friends and Influence People, and other various "motivational/self-help books".  

I am willing to bet that if you give him half a chance without being too hard on him.

I'm currently involved in programs like freedom mentor by Phil Pustejovsky and some rich dad poor dad content.