Which Updates to make?

[Zachary Watson]

My wife and I just bought a 3-family in Marlborough, MA, there is knob and tube all over the place, and we are planning on moving into the first floor. 

We want to update the 2nd and floors, and if we do it could be verrrry costly, possibly 16k for each unit to update electric and plumbing, we do plan on owning this for the long haul. 

What I can't tell is if updating the plumbing and electric now will cut down on future headaches, or will the headaches be caused if we have a few hundred more to pay monthly in loans on the renovations.