They'll essentially put a holey tube under the building, piped to the roof so the gas can pass through and escape without seeping into the building. 

In addition to the negative equity position, ADUs have other issues:1) the financing on an ADU is typically far worse than for initial investment property acquisition or is often not leveraged (HELOC, cash out refi, etc).

Although liability protection is offered by an LLC, insurance is also essential.

Additionally, in general, it would probably be good to find out how long the typical eviction takes in your area.

Teams are essential for local investing, but even more so for long distance investing.

What I just described is typical for A or B grade for me in Baltimore. 

That's essentially what the cash flow is on a good short term rental.

I don't see that it would add appreciable value for the appraisal or for rent, AND when you go to re-sell you would probably want to tear all that work out and put it back how it is now as your typical buyer is probably an owner-occupant and would prefer it as it is now.

Meanwhile the DST earns 3-6% monthly dividends, and if you're in a multifamily property it appreciates essentially equal to the general housing market.

I partner with people a lot but typically they are in a more passive role.