You mentioned beds and baths, but not square footage.

Does anyone have insight into whether appraisers consider livable square footage for ADUs in conjunction with the main building, or is it separately calculated? 

Comps should be within 1 mile (closer is better), sold within the last 12 months (more recent is better), and similar in bed/bath count and square footage (within 20-30% sqft). 

Getting it permitted would add a second livable space and square footage to the property. 

The second appraiser decided that he couldn't find any good comps, but used his judgement to give valve to the ADU, which resulted in the higher appraisal.I don't think that ADUs should be valued based on income or square footage, but I believe that ADUs definitely have more valve than they're getting right now. 

From the drone footage on the GRM web page it looks like development has (at best) just started, and this appears to be consistent with the single page development activity status report from GRM.

Speedy internet and a really good TV for those who need to view footage would be important, and an Apple TV for easy casting of video from laptop to screen. 

Get on the MLS and look for houses that have similar square footage and numbers of bedrooms and bathrooms that were sold within the past six months.

In finishing out the space and adding Heated Square footage to the home, you'll need to take into account Energy Calculations.

@Felix Torres As Steve said, if you occupy more than 50% of the square footage of the building, then you will be able to at least be eligible for SBA financing, though it will really come down to whether your business EBITDA and any other personal income can support your loan payments (look up debt coverage ratio) and your personal expenses.