High demand and still relatively low entry costs. 

@Geovanni Cano sellers don't like FHA, it is meant for people with little money and very low credit score, plus you have an FHA inspection which can derail a deal a week before closing, nothing the buyer can do.

Time overcomes low cash flow to some degree... rents go up while your mortgage stays the same and your tenant pays down your mortgage.  

I have a lot of colleagues with multis in Philly and all are doing well because of low taxes and high reliability, but it has its challenges.

I was initially drawn in by the low fee, which has since fluctuated, but may still be the lowest out there.

I applaud you for putting it out there but 1) maintenance/cap ex is far too low for a duplex 2) no PM. 3) vacancy at 1% will be challenging if achieving near market rent.

Additionally, since my parents are nearing the retirement age, I'd like to prioritize low-debt, high-cashflow deals.

Rates are usually in the high 8s or low 9s, and you are likely going to pay 3-4 points for these loans. 

High credit scores and low DTI are often required…and these take much longer than I first thought…Navy might take 45 days to get through the gauntlet.  

Looking at this mathematically, if you assume a 50% non-renewal rate (industry standard) and use the low end of the range of $5,000 per non-renewal, there is a loss of $50,000 per year on a 20 unit property.