Structuring my first investment property - rich uncle investor

[Gregory Jacobs]

Background:  I am a 31-year old New Yorker who is looking to purchase an investment property in/around New York City.  I recently purchased a fixer-upper apartment for $500k (20% down with a 2.65% for 10 years, then adjustable) and spent a substantial amount of my cash holdings on an ~$80k renovation.  The apartment is gorgeous and probably worth $700k - $750k.  I have $27k in debt (0% interest CC for another year), $30k in liquid investments, and about $55k in a 401k.  I make $165k/annually and I max out my 401k.  

Target: While I'd like to get rid of the outstanding debt as quickly as possible, I also want to set my sights on building wealth through an investment property in the Hudson Valley (or Poconos, etc.).  I'd rent the property out on Airbnb and potentially use it if/when the home isn't rented.  A respectable home ranges from $350k - $650k.  This will conservatively generate $6,500/month or roughly $3000/month in free cash flow.  

Question/Ask:  I am looking to take on an investor(s) to help finance the purchase and get things going.  I am fortunate enough to have a few family members who'd be willing to contribute to the deal, but I don't know how to structure it.    For simplicitiy's sake, let's say my uncle is willing to invest $100k to get things off the ground.  I will manage the property and invest $25k as well. 

How do I go about paying my uncle back/structure the deal so that he gets a fair return on his investment?