Hey BP fam! 

I recently purchased a 2 story duplex and will be doing a few updates over the next few months. I am looking to replace the cast iron drain pipe with a PVC scheduled 40 4" pipe. I am currently shopping around for quotes and would like to get some insight on this job from the ones that have experience with this. I will be removing/replacing the dry wall to make the pipe accessible for the plumber, I would also like to re-drain 2 kitchens and 2 bathrooms. Each unit is 2/1 with the same layout and the drain pipe runs in the middle with the kitchen on the first floor and bathrooms on the second floor above the kitchen. I am assuming I will have to remove part of the ceiling above the kitchen to access the drain lines to the bathtub and bathroom sink.

Do I need to acquire permits for this job and what would be the best way to go about replacing the whole cast iron pipe from the roof down to the crawl space. Would it be a good idea to also replace the pipe going out to the city tap and to install a 19" clean out outside the foundation?

Let me know what you guys think. Please see pictures of the cast iron pipe in the crawl space.