Private investors or lenders to flippers is common practice as is the 50/50 split. 

A common source of Subject To deals is people in distress (foreclosure) who have a pending sale date.

Local/Regional STR owner associations as well as AirBnb and VRBO often lobby for common sense regulations.

And its very common these days if your putting minimum down which it sounds like you did to have negative cash flow the first few years..

@George RedHowey test is the best way to determine if it is a security and thus either need to file with security or do an exemption like a 506cIt’s basically 4 parts:An investment of moneyIn a common enterpriseWith the expectation of profitTo be derived from the efforts of othershttps://www.investopedia.com/terms/h/howey-test.aspSo in a jv is one person finds the asset and one renovated it or both are acting in some capacity and making decisions - then you could consider a jv, but if one is a money partner and that’s it then the profit is due to the efforts of others Not an attorney

I'd recommend connecting with more people in your community such as landlords and other investors to see who they are using for their services in hopes of finding reliable contractors and well as some advice to overcome the most common/obscure pitfalls.

. - Capital stack needs to be clear, with preferred equity (if part of the stack) clearly represented as what it is - second position debt that multiplies leverage on common stock. 

That includes interest on the mortgage, taxes, common utilities, insurance, and so on. 

Common areas don't apply.

Motel owners leaving at the property is common practice.