I am reading a Robert Irwin book which suggests buying a home every 1-2 years as your primary residence, and renting out the previous residences as investments.

and move into the former investment home and again never pay the tax while enjoying the tax free sale of your former residence.3.

I'm not sure that the residence we are currently staying in is optimal for an AirBnb. 

Considering the rental income, her D/I will be around 20%.We are looking to buy a new primary residence for us.

A non-resident alien investing in the US adds wrinkles to tax compliance not encountered with your plain "vanilla" US citizen or resident alien tax return. 

Can we Non Resident Aliens use Standard Deduction now, as it is the only one left and in theory it should group the old Personal Exemption?

The resident is on a month to month lease.

I totally agree you don't need a LLC at this stage in the game.LLCs are useful in Hawaii in avoiding the HARPTA (5% withholding when you sell a property as an out-of-state resident), provided the LLC is registered in the state of Hawaii.

I’ve been in the mortgage business since 2003 but never turned the corner into investing (aside from a failed primary residence attempt in 06 - perfect timing, I know).

The support has been great and they seem to be planning enhancements to make it better for larger portfolios.