In general they will add the ADU only if it is existing living space such as workshop, bunk house, office, etc.  

He or she would then pay for the furniture for the space and pay movers to install it.

We need to go back and refi some just in one of our names in order to free up some space. 

I am planning to convert the living room in the property to bedrooms and want to use the garage as common space (have a pool table or a Foosball table, a couch etc).

Yeah nonrecourse is one of those things that exists in theory but is very, very hard to find in the residential space.

The biggest thing you need to analyze is how easy is it to release this space if the the tenant leaves. 

I had arguably 1,400 sq ft of crawl space incapsulated with the dehumidifier for $6,000. 

The traditional carriers you mentioned are not good options in this space.  

I know very little about legal precedent but I'd expect the major meter manufactures (selling into the utility space) to be well incentived to challenge these items best they can, and they have money.Here are the issues, and the reasons that the difference between an air forced system and a boiler/hydronic system are not meaningful for this discussion (ie efficacy issues of sub metering exist for either when method of measurement is measuring heat at point of delivery):In either case, the blower (or pump for a boiler) is the method of 'moving' either air (central air) or water/glycol or equivalent (boiler etc). 

If you're going to rent the space or sell it as livable space, it will need to meet code.