My first draft of a plan is to borrow in the neighborhood of $150K from an investor, put 5% down and live it in myself, and build a backyard ADU while putting sweat equity into the main house through tiling, replacing/refinishing cabinets, installing new flooring, etc.

You also can borrow from your 401k.

Pull it off the market immediately and fix everything, borrow money from a parent or friend if you have to, but fix it and give it a month off-market so it can reset.

In this case, I borrowed 90% of the purchase price AND repairs which meant I actually walked away from closing with a check from the bank.

If you do nothing with the remaining $65K and once you pay off the $35K you borrowed, then you're back up to $100K in "available funds" and you can start the cycle again.

borrowed from my local bank to purchase property and used my personal cash savings to build hookups and bathhouse office area.

I would ask to speak to past borrowers and past deal info.

You, as the borrower, transact with the IRA similarly to how you'd work with anyone else.

In this case, I borrowed 90% of the purchase price AND repairs which meant I actually walked away from closing with a check from the bank.

If you are borrowing money you just pay the interest.