Private Money Mechanics

[Harvey Yergin IV]

Background: 

I'm new to private money as an investor and want to make sure I understand the mechanics so I can build reliable models. Here's an example deal:

I purchase a property for $235,000 and expect $50,000 in repairs and $5000 in escrow/title expenses. Total cash needed for deal = $290,000. 

I'm confident I can refinance that property 6 months later at an ARV of $425,000.

I borrow all of the cash needed from a private lender and agree to pay 10% interest on the back end. 

After a cash-out refinance at 75% of $425,000, I'm, left with $318,750. I then pay the private money lender after 6 months their original $290,000 + 10% or $319,000 and I basically break even and make no money other than the monthly cash flow (money I didn't have before, I realize). 

Questions:

1. Despite the actual numbers, is this a reasonable and/or typical private money deal? 
2. Is a "10% deal" normally independent of the pay-back length? Is "10%" an annualized percentage rate or a flat rate of return? If I pay her back in 6 months, would I actually owe half of the annualized return rate or 5% of the total cash borrowed?
3. Unless I'm missing something, I need to find deals where the all-in cost is no more than 68% of the ARV just to break even or turn a profit, correct?
4. My only option to for making more profit (other than reducing the all-in cost as a percentage of ARV) is more favorable terms with the private lender (i.e. 8% return).

I found these numbers surprising since most of the BRRRR examples I read and hear about talk about all-in expenses being 75% of the ARV.

Thanks for reading and for any advice/clarity you may have.