I know it's making a lot of assumptions but I'm hoping being conservative shows this as something worth considering.

Residential Cost Segregator® by www.kbkg.comCost Segregation Software Designed for CPAs, Tax Preparers & Building OwnersThe Residential Cost Segregator™ is an online software program that allows CPA’s to generate custom reports in just minutes, providing tax benefits to clients without hiring a specialist.

Using the BP calculator and a lot of research about rental rates and ARV in this area, my worst case assumptions are not that scary (I.e. leaving up to $10k in the deal - at worst).

Be fair to your customers and treat them with respect.

First off, the question is slightly more complicated than what you've laid out, but still surprisingly simple.Your state law, local custom (i.e. what your judge says), and your lease all play into this. 

Superior wall foundation, unstained oak floors, custom mill-work, custom transitional tile flooring in mudroom and butler's pantry.

Cash invested: $20,000 This was an assumption.

If you want something custom tailored for something and the diy approach isn't great, they offer an API (https://developers.podio.com/) that is pretty feature rich and already a part of your account that most developers would be able to get you something pretty custom and as basic / feature rich that you would want.

Since I wear multiple hats I’m able to have low overheads and costs savings to my customers.

Be honest with your customers.