Short Term Rental Tax Loophole for Physician

[Dane C.]

I'm a physician with a fairly high W2 income (and thus high tax liability). I've wanted to get into real estate for a while as a means of diversifying my assets and reducing some of my tax liability. I'm facing a $280k tax liability this year ($205k federal). I have been looking into buying some multifamily homes and using the STR loophole to claim passive losses against W2 income and had some questions about this, including the legality of it. This is mostly a thought experiment at this point so below is the case:

The property: A newly built $1MM multifamily home (3 units)

The Case:
I purchase the property this year. I do a cost segregation study and claim bonus depreciation. I put it on airbnb as a short term rental. I meet the requirements of material participation. I claim the passive losses against my active W2 taxes. I convert the property to a LTR the following tax year.

Questions:
1) Are cost segregation studies worth doing on newly built multifamily homes or is it specifically for businesses or business type properties? Is this a case by case basis?
2) If I own the property for part of the year, is the tax deduction prorated in any way?
3) After the upfront depreciation is taken and the STR loophole is used, do I need to continue with the unit as a STR or can it then be converted to a long term rental (LTR) for the following tax year (or at any point down the line)?