Late payments  are the biggest red flags IMO.   

I have 300+ rentals and in my experience, over 80% of tenants with multi-year leases fail to fulfill them.Your biggest mistake is that you've set standards and now you're already trying to circumvent them.

I'd love to ultimately be able to do the BRRRR method, but my biggest hurdle will be getting loans without being a W-2 employee. 

I've put in a few offers but, no luck yet though.The Houston MLS is a great source of deals, at the moment. 

I wouldn't trust a form you find online and partnerships like that are the biggest cause of nasty litigation in the business.

Cashflow is going to impossible if you are unwilling to put in hours to source a deals and put up a lot of sweat equity.For me my sweat was better off put at my day job and buy out of state rentals that cashflowed.

I'd like to know what were some of the biggest challenges you had to over come, starting out in your REI career?

List Source?

I have a Purchase and Sale Agreement I use all the time (sourced from a closing agent many of us use in GA). 

Has anyone purchased a pre foreclosure list from list source, and marketed to it ?