If I put this in the stock market, I would need to make a return of 3.14% to match what I’m making in rental income.Some variables include: fluctuations in the NYC rental market and value that properties may appreciate, increasing NYC taxes and condo fees, fluctuations in the stock market, maintenance costs that will be needed in the next few years that will not do much to increase the value of the properties.I am not interested in leveraging these properties to buy a third.

Especially since you mention BRRRR - given the renovation component, you should get the property at a discount and create some equity buffer that allows you to absorb any fluctuations in value to the downside. 

It is helpful to know the current rate, it will fluctuate somewhat daily, but you can get pretty close with your calculations if he will just give you a number. 

If you are ok with the fluctuation, a HELOC will probably be easier, and as @Ruth Lyons mentioned, you can use it multiple times which would save on closing costs versus refinancing multiple times. 

Steel and anything with petroleum also fluctuates with the volatile market (asphalt roofing material.)In the current market conditions construction is a very risky business.

Your responsibility is to maintain the home, not preventing fluctuations in the oil industry.

Over the next year, how do you see the cost of renting vs owning a property fluctuating?

Plus, they fluctuate daily, so what's being offered today most likely won't be tomorrow unless you lock it in.

I find recent sales in the same neighborhood as my subject property because in NJ, prices can fluctuate a block or 2 over. 

Between the market fluctuation and improvements I've made on the home in the last year, the value has increased by at least 18%.