I'll just add on to make sure the land you buy doesn't have any fatal flaws before you close on it, i.e. make sure there are no weird things on title, i.e. easements, encroachments, and that all the utilities that you need are there, and it has legal access, etc.

If your friend just wants to be the bank and park his money for a guaranteed rate of return then I think 10% is fair and pay it like a dividend. 

It's hard enough borrow at regular mortgage rates and generate cash flow. 

I'm assuming that with your hard money interest rate will make that a pretty high monthly bill.

All 3 units were occupied very quickly and the property is now cashflowing above our projections with vacancy rate (so far) below what we expected!

Our broker mentioned that the average interest rate is 7.5-9% and they have never seen the rates drop below 7%.

Marie is an old city with a high vacancy rate, declining population, poor tenant quality, and will never see any meaningful appreciation.

The only downside to these is they are typically higher interest rates and shorter terms. 

So one by one they halved the values and almost doubled the tax rate.

After doing this, I then run the property through Airdna.co and/or Mashvisor.com  Both of these tools will give you projections of what type of rental rates, price per night, bookings, occupancy, seasonal variations, etc.