@Vidit Maini Starting your business as an LLC taxed as a C corporation offers flexibility but involves double taxation unless you elect S corp status, allowing profits to pass through to your personal return.For tax savings, deduct startup costs, track business mileage or vehicle expenses, and consider a home office deduction.

Cost segregation utilizes the MACRS approach.

Quote from @Francisco Solano: I suggest you ask a business attorney in your state for this basic template.

WHAT IS A COST SEGREGATION STUDY?

However, I still struggle to understand the art of estimating rehab costs. 

The LLC is there to protect you from liability when doing business by SEPARATING your business from your personal.

They do not take into consideration the revenue from the STR business as part of the selling price.So if comps say the duplex is worth 500k, then it is worth 500k.

Those things won't matter if your business crushes it.

Others investors drive extra ROI by thing like ability to reposition property for greater profitability and or less risk; ability to rehab property at less cost, ability to identify areas where gentrification is likely to occur, etc. 

It’s online only but purpose built for business owners and they have automation for those applying the Profit First cash management system.