What I would be concerned with is if you can lower your cost of living.

question can I roll renovation cost into the DSCR loan?

A roof on a typical duplex may cost $8k to tear off and replace.  

The wear and tear on hardwood floor - carpets has no recourse beyond the deposit damage if there is pee or replacement costs needed.

In your case, this appears to be $800k - $600k = $200k.You made no mention of the rehab costs.

The buyer can add a performance deed to the transaction which basically states that if the buyer defaults on the loan, the property is transferred back to the seller without a long and costly foreclosure process. 

Remember, that it costs money to refi...if its a small amount of juice to squeeze, I would just run your numbers to take a look at what makes sense for you and your journey. 

So they'd loan about 450k if your ARV is 1M (assuming this ARV is accurate), and then you can get a gap lender for the difference (180k plus closing costs/points/etc, holding costs).  

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What is the average cost for purchase, installation, and the associated app?