I believe the appreciation has been great over the past couple of years and prices are lower than in major areas like Miami metroplex or Charlotte.

:Class A Properties:Cashflow vs Appreciation: Typically, 3-5 years for positive cashflow, but you get highest relative rent & value appreciation.Vacancy Est: Historically 10%, 5% the more recent norm.Tenant Pool: Majority will have FICO scores of 680+ (roughly 5% probability of default), zero evictions in last 7 years.Class B Properties:Cashflow vs Appreciation: Typically, decent amount of relative rent & value appreciation.Vacancy Est: Historically 10%, 5% should be applied only if proper research done to support.Tenant Pool: Majority will have FICO scores of 620-680 (around 10% probability of default), some blemishes, but should have no evictions in last 5 yearsClass C Properties:Cashflow vs Appreciation: Typically, high cashflow and at the lower end of relative rent & value appreciation.

I would like to have lower monthly payments should I make a big lump sum payment towards my principals and ask my mortgage company to adjust it or refinance it or which one is the best ? 

Local banks typically offer lower interest rates but might require a solid track record and detailed financials.

that we’ve learned in our 24 years, managing almost 700 doors across the Metro Detroit area, including almost 100 S8 leases:Class A Properties:Cashflow vs Appreciation: Typically, 3-5 years for positive cashflow, but you get highest relative rent & value appreciation.Vacancy Est: Historically 10%, 5% the more recent norm.Tenant Pool: Majority will have FICO scores of 680+ (roughly 5% probability of default), zero evictions in last 7 years.Class B Properties:Cashflow vs Appreciation: Typically, decent amount of relative rent & value appreciation.Vacancy Est: Historically 10%, 5% should be applied only if proper research done to support.Tenant Pool: Majority will have FICO scores of 620-680 (around 10% probability of default), some blemishes, but should have no evictions in last 5 yearsClass C Properties:Cashflow vs Appreciation: Typically, high cashflow and at the lower end of relative rent & value appreciation.

You may FEEL that they are but your expenses may go UP at the same time as rents need to be LOWERED!

If I have lump-sum free cash, should I just apply it to my mortgage to recast so that my monthly goes lower?

That way your purchase price will be lower and your debt will be cheaper due to inflation.  

Contained within the the email was a 5 Minute video featuring @Dutch Mendenhall providing a tour of 4488 Livingston Street, a single family home I can best describe for those not familiar with Philadelphia as located in a "C" neighborhood with no barriers of entry. 

Seems like it's in a lower end area so if it is filled you will have tenant issues and turnover cost.