Strategy for multi-unit plumbing upgrades

[Abby S.]

In the planning stages of a single unit rehab in an a mostly original 4 unit building that I own in an "A" location - Wicker Park. I've spoken to a few plumbers regarding strategy and would like to renovate one space at a time to spread out costs and mitigate lost rent of having tenants out. 

To do one space, I'm stuck with the awkward locations of the galvanized steel plumbing stacks, which limits flexibility of let's call them "modern layouts". It also prohibits addressing issues like weak water pressure at the source. Suffice to say, the analogy is doing a paint job on a unique car - but leaving the mechanicals in place without addressing reliability. 

The other part is that in doing any single unit work, it appears likely that walls will be impacted in the below floors, if at least for plumbing access - which is an issue while tenants are in. 

So the developing perspective is that by doing one unit, you do it at a time when all are open - and move to PVC and address it as a system for longevity. Makes total sense... however: That's a difference of starting with $15-20k a unit in plumbing, to a factor of 60k for all three and probably upgrading the service because you've got inspectors looking for a job properly done. Moreover, let's make that job $75k, conservatively - and months of foregone rent, so I'm at $100k just because I wanted a modern bathroom. 

And at that point, I haven't even touched the kitchens which are part of this too. 

So how would you think about this one? Looking to keep the building long term - but also anxious of what will balloon into a really large project. That said, it's all a balance of how much money to put in, and letting it work for you. Bathrooms/kitchens are the biggest bang for the buck for rentals - but it requires addressing what's behind the walls. I'd love to have as much cash on hand during the next wave of economy changes and looking for new deals, but that's another factor. 

Do you think it's worth starting small, piece mealing and managing costs - or going all in?