I've accepted that I will take a significant loss on this, and have already learned a ton from it, but I would like to reduce the total loss as much as possible.

Proc. 2013-13, 2013-6 I.R.B. 478 (February 4, 2013)Report on Schedule E, not Form 8829Allocate expenses if managing multiple propertiesCaution:   those Home Office Deductions cannot be used to increase your losses!.

I have  a W2 job and look forward to the losses this year to offset some of my income (Not my 'WHY' for running an STR, but a nice bonus).

This creates two loan payments ($100,000 of equity and $300,000 on the new mortgage).Key NumbersHome Equity Loan Interest Rate: 6%Mortgage Interest Rate: 7%Rental Income: $3,000 per monthExpenses (management, taxes, insurance, maintenance): $800 per monthIncome and ExpensesMonthly Rental Income: $3,000Monthly Expenses: $800Monthly Mortgage Payment: $2,000ExplanationThe investor earns $3,000 in rent each month.They pay $2,000 on the investment property mortgage and $800 on other expenses.This leaves $200 profit each month or $2,400 per year.However, you have to pay $6,000 interest on the equity borrowed.This leaves you with an annual loss of $3,600.While the rental property generates positive monthly income, the interest cost of borrowing the initial $100,000 results in an overall loss.

Any tax knowledge of if people doing this strategy are able to take the losses from the cost seg study (on the ADU) to offset their W2 income?

One of my goals is to go through my past tax returns, and figure the ROI my rental properties with taking into account the tax savings (I typically calculate the ROI on net cashflow at the end of the year)I have a W2 so I generally aim to maximize my pre-tax accounts - 401k, HSA, IRA to a backdoor Roth IRA, 529My "losses" would be passed forward since I don't qualify as a RE professional nor have active RE losses.

Warning:If you depreciate a property down near zero and then have to sell your property at a loss during a situation of distress...You could end up giving all the proceeds to the bank AND owe the IRS a big chunk of money for recapture.Long-term tax planning with real estate needs to be coupled with risk management and making sure you don't lose any properties.

You could also reward staff for lease renewals, positive guest reviews, and reducing unnecessary expenses.

To give you some hope, in the mean time of your RE losses, many of us are doing very well. 

Here is my Cliff Notes on this elaborate example:If you have unused losses from the past, they might significantly soften the tax blow from a profitable sale.I don't see how this is called "strategic play" or "premium lemonade."