I do like the idea of buying a home where everything is still under warranty, although the idea of buying something that doesn't exist yet gives me some pause.

We have an existing 5 car garage which I plan on converting into two ADU’s, and an existing 400 - 500 sq.ft conditioned space that is currently not being used for anything.

definitely. i have got the details from them for their existing landlord. however, that name does not match the owner on the city tax office property records. and they have confirmed that they provided the landlord's details, not the property manager's details.I believe that should match or it is possible to not match?

When adding a second rental property to an existing LLC, you can generally deduct start-up costs and operational expenses. 

Not as much as multifamily but still more than STNL single tenant or 2 to 4 tenant type retail center properties.The larger centers they live or die by the anchor tenant so really have to know if that tenant owns or lease the space, when it was last re-imaged inside and out, and what sales they do per sq ft year over year and how they have been trending.Larger retail centers have defaults from smaller tenants with covid right now to work through so offering should have reserves built in for some not making it so buy in cap rate on existing NOI might go down in the short term as tenants are lost and tenant replaced.

What type of loans exist for those looking to owner-occupy a non-warrantable condo?

Commercial lending terms would apply.The 80/20 or 80/10/10 loan types are no longer in existence.  

Limited new supply additions suggest that existing properties may continue to enjoy favorable market conditions.5.

Subject note wraps around an existing 4% interest 180 payment $615,000 mortgage.

They have considered changing these rules to help lower insurance costs HOWEVER, they would grandfather existing owners - at least 50% use as short term rentals so changing these rules wouldn't fly otherwise.