I currently live in New Hampshire, and have one cash-flow positive duplex- which I scrimped and saved years for while building credit.

If the systems are in place to weed out the bad applicants, IE the ones with evictions, transient history, poor credit, poor job history, etc, then you shouldn't blame the PM when a tenant goes bad.

I have money saved up and also have a line of credit I could use for the initial purchase and rehab. 

@Corey Cetto contact as many local credit unions as you can.

Work out a payment plan to get back on track.

Who are you defining expenses and who keeps track?  

For a multiunit the rent from the other units would be credited to you on the purchase loan, so as long as you find a good property you shouldn't have and DTI issue.

After talking to 3 different big banks who said "No due to seasoning requirements," I finally got my credit union to refinance with no cash out on the home my parents deeded over to me 3 weeks ago.

That means that they can't deny an applicant because he seems like a jerk as long as he meets the criteria that the landlord set out when he started the screening process (credit score, income, job stability, etc.).

I have no paperwork or agreement with the previous tenant, but, I was provided a deposit credit from the previous landlord upon closing that was writen into the purchase agreement.