We recently acquired a commercial building in CZ4 that is half-occupied by my wife’s business.  While it seems like an overall good investment it is not helping our cash-flow, so improvements must somewhat pay for themselves or provide a clear benefit to health, safety, or comfort.  

The property is technically 4 connected buildings, three of them with two stories.  The front is an old farm house (probably Civil War era) and the rest was built in the 1980s.  That newer parts are 2×6 framed with truss roofs.  All the foundation is slab except for a small basement under the oldest part.  There is a gas furnace in that basement, but I believe everything else is on forced-air heat pump.

Ideas so far:
Idea: Attic insulation is only R25–increase this.
Problem:  Not going to save much money.  Existing insulation already at top of soffit baffles, so those would have to be extended.

Idea:  Air seal ducts in attic.
Problem:  This seems difficult since they are half-covered in cellulose.  Aeroseal?

Idea:  As individual heat pumps fail (one looks quite old), replace with VRF models.
Problem:  Would this also require new air handlers?

Idea:  Blower door directed air seal enclosure.
Problem:  Cost?  Finding a contractor?  Ceiling is probably leaky, but how do you fix that with cellulose in place?  Aerobarrier for the currently-empty floor?

Idea:  Remove fluorescent ballasts and direct-wire troffers, replace tubes with LEDs.
Problem:  Not going to pay for itself (unless maybe I DYI it), makes trash of working fluorescent tubes.

Idea:  Improve filtration, Add ERV
Problem:  Does not address a known issue, just seems like a good idea.  No payback.  Probably expensive.

We’ve been told the roof has about 10 years of life left in it.  Does a roof replacement open up any opportunities for improvement?  

Any thoughts on these ideas or additional ones are appreciated.