There is this crazy mix of factors contributing to the East TN success that I am having a hard time find elsewhere.

I would be interested in joining, if it's open to anyone to contribute.

He owns a majority of the building (65%), however due to the breakdown of the association fees, he currently contributes about 40% of association fees.

My friend and I will be partnering on this deal with 50/50 contribution.

Or at the very least, (1) consider getting a loan to cover these expenses and/or (2) be mindful of these unexpected costs throughout the project.Pre-Deal Marketing fees, training, learning market, travel time including gas mileage, costs for purchasing legal forms & contracts, fees to start an LLC After Rehab Deal is Accepted HML origination fee, HML points, Buyer closing costs, down payment, title company, local taxes (transfer tax, prorated property tax,etc) After Buyer Closing Dumpster rental & permit from town, buiilding permit for construction, monthly holding costs to pay back HML, homeowners insurance, repair expenses prior to being reimbursed from HML, Marketing fees to promote 'coming soon', dream team fees such as CPA, attorney, and fees to pay for the SOW inspection Seller closingSeller contributions, agent commissions, prorated property taxes, title company, attorney fees 

I was using the BRRRR calculator and wondering: what are the biggest contributing factors to the Cash on Cash ROI calculation?

Seller can contribute up to 6% CC (based of purchase price, not as-is value).

With the $20K contribution and the same 20% compounded return, over 10 years, you'll have over $700,000.Btw, if you invest that $700K earning 12% cash-on-cash return in a long-term rental property, you're now earning $85K per year, completely passively. 

Much of that will normally come from a really good buy and also a significant capital contribution from you, a partner, combination. 

You could also try partnering with someone that does have proof of income and split the equity or pay them a fee for their contribution to obtaining financing.