Is an SDIRA my only option if I want to use the funds for investing in real estate?

While it's not rocket science, it takes a certain personality to find it enjoyable and not frustrating.  

This year might not be the best year to go all in with an investment if the sole goal is cash flow or appreciation (not personal use).In a mature market such as the smokies, I think you can reasonably arrive at a fairly narrow occupancy rate. 

What deals have you done and what type of funding sources and why?

If I have to boot someone I'll have it re-rented for more money in a week and the person getting booted will probably be living under the bridge as they won't find anything as cheap as me. 

They are holding funds so they can live in the float as long as possible, probably because they don't have the cash to pay up.

You can define the roles of each person inside of the partnership agreement without necessarily using the terms General & Limited Partner. 

Depending on income and credit there are always credit card, personal line of credit and personal loan options available out there

I'm no longer a W2 employee so I am not currently contributing any funds to it. 

I work at a hedge fund, which allows me to save a good bit of money.