I was originally planning on using PEX. But, in this case, I decided against it.
The way the layout is set up, it turns out that it wouldn't make sense to try to do manifolds and a home-run type of setup. One reason is that the existing plumbing goes up through the walls etc. to each apartment and it wouldn't be practical to try to do new home runs to each fixture.
It also turns out that the cold water coming into the property is in the front of the building and the utility room where the 3 hot water heaters and
3 boiler/furnaces are located is in the back of the building. And, all of the fixtures for each apartment are in the middle. So, rather than running the supply from the front to the back, and putting in 6 manifolds there (3 hot and 3 cold) for home runs, I decided to use a more traditional plumbing layout.And, another reason for not using PEX is that there are some sharp turns required in a space where PEX bends would not fit. And, if I did the PEX with fittings etc. to make the turns, the cost of all of that would be a lot more than just using CPVC pipe and CPVC fittings.