The issue I had was that most lenders required a certain number of completed flips done under a LLC.

.: I haven't passed this past legal review so for what its worth: Part of my standard requirements for everyone include income is at least 3X rent, minimum credit score, say 640, Clean record and no evictions as well as deposit is paid in full at signing of lease and 1st month rent is paid in full prior to handing over the keys.

Buyer's agency agreements were already required here before, our regulatory agency just went from strongly recommending them be signed right away but not really requiring them until writing a contract to 100% requiring them to be signed prior to showings.

Hard money lenders are much more like banks and come with many restrictions, requirements, due diligence, fees, etc.

So this requires some upfront planning. 

I don't know if this is required in your locality but if it isn't get rid of it.

I have just started in a 3-day training for the Lee Arnold broker certification program and thus far just completed the online material required for preparation. 

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

That would probably require a professional. 

Just my personal opinion - get a mentor or a person who already has good experience running STR business, preferably in your area (but not 100% required).