I have an opportunity to JV with 3 other investors and I want to know how best to spread the risk and reward, fairly, while securing everyone’s stake by the real estate.We’re looking at a potential deal that looks like this:ARV: $400k-$425kMOA: $165k RB: $160kTarget net profit: $75kConstruction time: 6 monthsInvestor #1 has the acquisition funds.Investor #2 has the repair funds.Investor #3 is the General Contractor.Investor #4 (me) is the Project Manager & Listing Agent.If the GC and I waive our fees in exchange for an equal percentage of the net profit will that be fair?

These sellers are motivated (as a percentage) and glad to have someone offer lease and option to buy some years down the road to build equity. 

Not sure what type of agreement you may have with this gentleman but some questions that come to mind are: what is your ownership percentage in this project and is that reflected in any contract? 

You will also need a certain percentage of the unpaid balances on your other loans as reserves in order to qualify.  

His percentage he would get off the flips was his income.

If i need to come up with my own money to get started how much and at what percentage.

He has likely been paying a hefty percentage of his monthly payment to interest over the past ten years and is only now starting to see the scales tip in favor or the principal vice interest.

I ask because, even when using market rates, the results I get from each model vary greatly.For instance, when modeling expenses as a percentage of the rental rate, if expenses are assumed to be 50% of rental income, I must have a rental rate of 1.0% of the purchase price to cashflow:However, if I model expenses as a percentage of the purchase price, even if expenses are assumed to be 1.6% of the purchase price, I only need a rental rate of 0.7% of the purchase price to cashflow:I assumed a purchase price of $350,000 in the spreadsheet: at 0.7% this yields $2,450 in monthly rental income, while a rental rate of 1.0% yields $3,500, a huge difference of $1,050 per month.What are your thoughts on the analysis and models?

I am aware of two methods for estimating expenses: using roughly 50% of the monthly rental income, or using roughly 1% (or some other constant percentage) of the value of the property. 

If you purchase a residential income property - like a 2-4 unit - you may be able to apply a percentage of the gross rents to your income, however, some lenders like to see two years of landlord experience to do this - check with your lender.