It's a tax on the gain.How is this calculated?

Have you played around with the savings calculator to give you an idea what your cash flow needs to be?

@Saad D.It's not dead, but it also doesn't calculate the MASSIVE elephant in the room....EXPENSES. 

There really isn't enough information here for someone to give you a proper answer.What you need to do is calculate those tax savings over the next 5-7 years (or however long you plan to stay in the house) vs. what the interest rate reduction will save you over that time period.

If a duplex / multi-family home, how do we assess/calculate potential rental value?  

BiggerPockets also has a calculator to analyze deals, and I highly recommend you start this as soon as possible, even if you are not ready to buy.

My goals would be to increase monthly cash flow and have more access to the property's equity for things like Cap Ex, etc....Here's a blurb from a lender's website:"By combining banking functionality with home financing into one dynamic instrument, borrowers are able to save tens of thousands of dollars and years off their loan""Designed after popular programs around the world, the All In One First Lien HELOC is the nation’s first transactional offset type-mortgage program.Home financing and banking combined:Deposits lower your loan’s principalFunds remain available for expensesInterest is calculated on the average daily balanceThis lowers the monthly interest paymentsTens of thousands of dollars can be saved over the life of the loanMortgage freedom can be achieved in half the time or less

If you're looking to invest in Jerome Village, definitely factor this future charge into your cash flow calculations and maybe have your CPA take a look at the exact language in the Declaration. 

DSCR stands for Debt Service Coverage Ratio, which is a calculation that determines if a loan's income covers its annual debt service. 

Here's a bit more in detail about how rates are calculated for DSCR loans:1.