DSCR is a no-income verification loan.

If you’re not using a primary residence loan then I’d go for the triple because it would likely cash flow better than a duplex

Redoing floors (3 floors), soundproofing between levels, and mini split install

I used a conventional loan and put down 5%.

She even wanted to tell me exactly where to install it. 

Financing is a different situation when you have entities involved, meaning that commercial loans need to be used rather than what you have already experienced with a conventional, FHA, VA or other "regular" mortgage. 

I recently came across this "FHA construction to permanent Loan" option which seems almost too good to be true, so I wanted to get some input on how this works and where I might be able to find a lender.

I took out a construction loan 2 yrs after the purchase to rehab it.

If we installed such higher end finishes, and anything ever needed repairing.

In that case, you will need the lawyer to draw up the note and associated paperwork.I'm not exactly sure what is meant by subject to financing, but that sounds a lot like a finance contingency, where in the buyer is allowed to bail out of the contract if they can't get a loan.