The heat coils can address this.

New Lineset will be ran through attic and new coil will sit on existing furnace.

I would suggest the partition walls be framed out of metal building materials with metal panels on each side, so it would be easy to take down and store if a tenant wants a bigger area.Insulation wise, go with the standard metal building insulation on the roof and walls.

Sounds like it might be...may be time for bars on the windows and metal security doors?

Handicapped accessibility, exiting, fire protection (metal studs, other non-combustible materials) fire sprinklers, insulation, lighting, HVAC, all will be somewhat different for commercial spaces.

It's a metal and brick building... the dude is crook and a con artist.. 

There were never any complaints about mold and they also forgot that they are responsible for changing AC filters every month, cleaning the AC closet door and also when the AC was repaired, it was also professionally serviced, coils and condenser fins cleaned. 

That's a first impression thing, and I believe a nice heavy black metal railing will possibly allow a better renter to be interested in the place vs the handyman special.

Here's a '78 one we're trying to remodel right now:The roofs were a rolled metal material laid over a very lightweight and flimsy 1x2 and 2x2 truss system that was extremely fragile and vulnerable to damage from falling tree branches, hail, and if a repair man didn't know how to walk on them the trusses were easily broken. 

“I’d love to throw a hair metal-themed party in here,” she jokes.