@Jack CallinanBe mindful that owning a house-hack with more than one person(who is not a spouse) does add a lot of complexities to your return.First, since it is owned as tenants in common by two individuals that are non-spouses, you would each need to report the activity on your return.2nd, it is a house-hack - House hacking makes your tax situation more complex.You purchased a property that is treated as both an investment property and a personal residence.

The "layover house" that you alluded to is commonly referred to as "crash pads" in the airline industry.

I kept taking damage to my health bar, which was my bank account and I needed a solution.  

So yes, typically you will need all plans signed off on by a P.E.The third common component is a study showing that the additional fill placed in the flood zone by your planned building will not significantly decrease the water holding volume of the floodplain (in addition with other permitted or built fills in the same basin).

My question is - Is this something commonly done? 

Do I need to form an LLC before I have a deal, what are the terms I need to expect, like # years, common rates %, LTV for commercial?

This is one of the ways we all learn is by asking questions.The 6 month seasoning period is very common.

A general valuation formula many in the industry use is: # of economically occupied lots * monthly lot rent * 70% (assuming 30% of income goes to expenses, common for parks on city utilities) * 12 (months in a year) / desired cap rateFor this park at a 10 CAP (many parts go for lower cap rates now, but small parks might still go for a 10 CAP), that makes: 21*298*.7*12/.10 = $526K . 

Is it possible to also write off the other common deductions (PMI, interest, depreciation) while living here? 

Some people like the 1 LLC per property since its common to name the LLC the street address for the property.