The property taxes will be on his Schedule A during the time the property was his primary residence, assuming he itemizes.

Of course you can get discounts for having certain items FULLY updated, like plumbing.  

We understand that not every negative item we dispute will come off.We persist until we succeed because you must have a high-level of doggedness as a real estate entrepreneur.We understand there will be sunk costs and time being wasted.

Also, how old are your capex items? 

My family makes a joke about how those items aren't "Nickproof") At this point we decided to call it and come back tomorrow. 

The main issue is that to do the ADU you have to spend so much bringing other items up to code like electrical, plumbing, lighting (windows) and egress.

The best place to start is with a spreadsheet that has every every cost itemized. 

This is true for bonus depreciation items as well.  

The other business I run is reselling, listing items on eBay & FB.

I'm wondering how much specifics I need to include for each line item.