I depend on another department as well for answers and I too have to wait," and then asked if I would "be open to an installment of a partial payment?

Depending on your practice size and income level, you may just want to start with maxing out 401k and also adopting a defined benefit plan before committing to becoming a lifelong real estate investor.  

If you keep it as an investment property, a lot may depend on your location and condition.

Expect a custom ADU to take 9–18 months, with 3–6 months for design and permitting and 6–12 months for construction, depending on complexity and contractor availability, and the speed of processing permits.

That will be an important piece to this depending on how you plan to source your capital.

You missed an important item: Depending on how a person does #1 or #2, it could get them: A fast-pass to the "Principles Office" for "bullying" and now there sitting in "detention".... 

However the most obvious benefit based on what you’re stating is that the depreciation from cost segregation will offset your $100k in taxable income from your commercial rental.There could be more benefits depending on future plans especially if you plan to sell any real estate in the near future. 

Looks like anywhere from 6k to 10k depending .   

After that, it may depend more on the workload of the inspector.

@Phil SheltonYou would need a civil engineer to provide a drawing to get submitted to zoning and get a permit if it passes zoning is most common This also depends on the road - if it’s a state road forget it as it will take a year to get approved and cost a fortune - if it’s a local road process not as cumbersome but don’t expect this to happen quicklyIn some instances you may have to prepare sight distances etc to make sure it’s safe to add a curb cut