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.

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

The program was created to give low-income tenants an alternative to living in federal project housing.S8 sets their rental rates to the LOW-END of market averages, if not slightly below.

Also, for low value properties, most lenders wont take the risk. 

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.

Rents are low and prices are high.

A property could be cheap but be located in a low performing market.

If I ever run low on reserves, I can easily transfer funds from my personal to rental account.

For example you are putting in low grade laminate and all other listings are putting in high grade vinyl.

An emergency fund needs to be liquid, and immediately available to you in addition to being low risk and protecting principle.