Your question is should you pay cash or get a mortgage.The investment calculators will say you will have a higher return on investment using as little of your own money as possible.Depending on your goals, like if you want to buy more rentals, this may be a wise strategy to put as little down as possible.However, if you are strictly looking to maximize your cashflow, having a paid off house is great.Honestly, I have a bit of both but like having the house paid off.

Then calculate when you will need that roof and how much it will cost when you do.I do like that high appreciation potential, and this may work well for you.

(Full disclosure: almost always I used an agent.)Start by doing your first deal as an agent in order to get a better understanding of the business, then calculate your overhead/ operating expenses and you will quickly see what we’re all trying to tell you.

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

It really becomes a time value of money calculation based on when you want to sell your Class A rental.

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

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

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

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.

This is because of the memory size for transactions and the way fees are calculated.