I bought and lightly fixed and sold a property; I bought and fully rehabbed another house and sold; I bought a short sale and fixed it up as my primary residence; I’m in the process of a flip that has extensive work (just closed on Wednesday); I had a rental for almost three years.

I wanted to take this opportunity to hear what all of you appreciate most about this amazing platform.

We checked... this 401K will only loan on primary residence.

." - Did you use to live there as your primary residence?

I like your HELOC strategy for pulling money out of you primary residence then using that to buy another rental.

So, the bank assumedly "bought" the property at a "real" auction because (1) it wasn't happy wtih the bid amount, or (2) it wanted to pursue the owners for the negative equity, and needed the property to sell at the fair market value.That makes me think it is clear this is the primary lien. 

@Neal Collins I spoke at length with AppFolio because I don't have enough units to use the platform (50 minimum are needed), and my broker told me I can be added as a property manager and manage my portfolio separately, but after we looked into the system and how it would work for handling funds, they said that even though you can have separate property managers manage separate portfolios, you cannot have separate bank accounts. 

Your primary state of residence and principal place of business comes into play with many states. 

Can I claim that $5k first year startup cost deduction if it's for future rentals but is also my primary home?

Your parents have been living there but in order to qualify for sec 121 it must be your primary residence so screw the 121 it won't qualify and you'll end up really screwed :)  There is a safe harbor in Rev Proc 2008-16 that establishes 2 years as adequate.