I was hoping to refi in a few years and get cash back out at the new value after rents are increased.

Comparable sales on 3 Bedroom two Baths in the area is from $120,000 to $150,000 move in ready as this one is the $15K delinquency is PTI and increasing every month, and the owner finance buyer bad credit will not allow refinance as you suggested Jay.   

I also made mine taller, which should increase the stack effect and make them more efficient.

She agreed, I gave in to resistance and increased my cash flow.

Here are the numbers I've calculated  based on 80% refi of all 3 properties, at 30 years, at 5.25%:Item                              Current                 Post-RefiCash available         $        0                   $300,000 +/- Cash Flow/Year       $   65,000              $  52,000 +/- Re-invest $300k from Cash out as 20% DP on more properties (there's an even better way than this too)& using the same ratios of ARV to NCF, you could increase your NCF an added:  $78,000/year; to $ 130,000/yearYou are sitting on a Gold Mine here, and you're thinking like a "homeowner"...not an investor...although you're not alone.Your Options:  Limited by the maximum Cash Flow from existing properties after complete payoff Max CF/Year                                                                                    =  $   95kCost to do this (pay off all mortgages using your cash)          =  $  456kNet result                                                                                        = - $ 361K  (that's a loss)REFI ALL Option:  Limited by ???????                                                                                                             

I would talk to your CPA first.I have bought at year end to decrease my liability and or increase my passive loss from year to year..

Also, any good books I should be reading to increase my knowledge of real estate?

Most MFRs I've seen are at 0.6% - 0.8%.Look at MFR sales in South BostonIn 2013, there were 39 units sold, with an average price of $727,949 and 37 days on market.In 2016, there were 36 units sold, with an average price of 1,272,467 and 50 days on market.A 73% increase in 3 years.3 bed rentals in South Boston over the last 3 months averaged $3,346.I've felt for a long time that the better deals are found south of Boston in Plymouth and Bristol counties.  

Whatever income the new buildout would produce would increase your value.

Although it did not make sense for me at the time since a shorter time frame increases the monthly mortgage payment, the bank accepted the deal.