Kitchen cabinets do not all close properly, some windows still didn't open well, they didn't hire a foundation crew to install piers, they simply used some cinder blocks & shims (with no receipts), and no main line plumbing was updated. 

I have before for other rental properties when I installed new water lines.

I had a contractor install a range hood in a unit recently and install venting to the outside of the unit. 

I received feedback that service cannot be installed until Spring!

In fact, you might want to consider installing laundry hookups in each unit and requiring the tenants to provide their own laundry machines. 3 units is pretty small for shared laundry.

How can I tell if it is going to be cost efficient to get new windows installed.

Despite the feasibility of installing necessary equipment at the site affecting the decision.

Install a camera.

However if the problem is black iron or galvanized steel piping that has rusted through or a  copper line which has sprung a leak, it may be an harbinger of things to come {around here many systems were installed or repaired in the 1960s/70s using thin-walled copper pipe which, 50years later, has started to develop pinhole leaks}.

is pex possible to install without ripping walls out?