So, I took this approach with my first property. Hard money BRRRR that refi'd into a traditional mortgage. A few comments:
Do you know how much you can get approved for with a trad mortgage? This is extremely important so you don’t buy a house that ends up being too expensive for you to refi out of.
Yes, a cash out is still possible. Your hard money loan will 99% be structured as a construction loan on which you pay interest only, with a balloon payment at the end of the loan term. How you pay off that principal doesn’t really matter. You could flip the property, sell it and pay with the profits. Or cash out refi and get your loan paid off plus extra for your next project.
Your private money borrowed before the loan needs to be in your bank account at the time of the loan application. I spoke with over a dozen HM lenders and there’s not one I know of that would except a down payment from a third source. It’s showing that you don’t have skin in the game, and that’s risky for them. That being said, if you have an arrangement with a private lender already and the money’s in your account, they’ll be none the wiser.