We created chases, for the most part. The only plumbing lines that are enclosed are to the shower, and we made the wall panel removable in case we need to repair something or chase down a leak. The AC electrical is in exposed conduits and the DC electrical is behind a soffit.
I’ve never run PEX. I figure it’s good to run around the chassis. I’ve done lots of copper. I figure that if I keep all the PEX under the bus I’d have an easier time fixing it. IDK, maybe I’ll feel different once I start using it.