Hello Brian,You'll need to perform some calculations for this task.

So there are a few ways to look at this, the 1st question is are you sure your renovation’s will double the property value, most renovations on primary residences, your lucky to get 60-70% of the dollar cost back out upon sale, so really nail down your comps, than you have basically a math problem if your rate on your primary goes up how long if ever before that extra payment is more than 400k in taxes, that’s just a simple calculation to help you decide, but I suspect you actually have a different question here, from a purely financial perspective my guess is the best option is to do anything to avoid that tax hit, but one of the reasons to make money is to spend it on things that you enjoy, based on your overall financial picture and a subjective view of how much enjoyment you will get out of a renovated home, you should decide if you want to roll your profit into another deal or “cash-out” your winnings, I love cars and I’m willing to spend more than is fiscally smart on them because they bring me joy, there is nothing wrong with that, but i don’t think it’s a fiscally smart choice, without knowing your exact property id imagine a renovation would fall into that category, so that’s the terms I would use to decide.

The key benefit to a Dutch repayment schedule is that they are often easier to find, the approval requirements are lenient, they tend to close quickly, and the calculation is very straight forward easy to keep up with.

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

Again, this is a general rule when calculating a deal.

Generally speaking you will need several things to successfully complete a BRRRR: ARV - being able to calculate the Value on your own (meaning, without the wholesaler telling you the value) is really important. 

should this be good base line calculation for renting to them .  

Investors calculate closing costs into the deal.

This calculation indicates a need for a 1,400 CFM hood, which is hard to find in a ductless vent.

Your credit score will take a hit with the heloc and banks will sometimes count the entire funds available as though it were all used when calculating dti for other deals.