I've got a mixed use building with a vacant 5200 sg ft. medical space on the first floor.

I here in the Netherlands Rotterdam working on renovating a 3 unit building

If you have a building background, I would work with an architect and build some unique places that are stick built to hold the equity value better.

I am trying to tabulate Business that may have higher depreciation but yet help me build wealth in form of real estate or potential customers for variety of services. 

Quote from @Breland Clark: I would like to know more about developing land and subdivisions for new builds and apartment buildings. talk to the land development arms in your city or state.

As long as the ADU is under 900 sq. ft. and meets the state building code, there will be no variance or special permit needed, so no ZBA or neighborhood meetings.

I would avoid new build properties from southern impression homes.

You should reach out to @Melissa Haworth she can get the actual numbers/rents on STRs in the area to help run your comps.Each building is different, each area is different, it is important to find accurate data to make good decisions.

The building has some deferred maintenance that I have been dealing with.

I would assume that it should be blocked off with some type of decorative tile or something of that nature.