Ideally, I'd like to tear down the entire thing, but I'm assuming we need some 2nd form of egress for that floor.

By trashed, do you mean it is uninhabitable or does it just need some deferred maintenance such as flooring and a roof?

So, if you planned to own it for 30 years you could be relatively sure that you will replace the:  plumbing, windows, siding, floor joists/piers, and roof (again) . . . that's not touching aesthetic/cosmetic things that will possibly be replaced along the way. 

Let's assume 1500 sf flooring in each unit. my area it is $6 sf to replace.

I have a headache pier and beam foundation SF home that ultimately required a $30k complete redo of the foundation and flooring in the beginning of April.  

I've had PMs send "technicians" to check a guest reported  problem that have resulted in requesting that I replace a dryer that just needed a $75 part, calling a $300 electrician who finds nothing even after I tell the PM that there is NO wiring within 10 ft of a guest reported "hotspot" in the floor (say what?)...

Some properties still have the original Slate Roofs which are costly to replace. 

Countertops and vanities replaced, cabinets painted, new flooring, new appliances and some new fixtures.

House is divided in to one unit top floor, one on main and two units in the basement.

Account ClosedThere's a limit as to what a handyman can do, certain jobs will require professional plumbers, electricians, flooring guys, etc...