Hi Mathew,
A lot of these answers will depend on what your standards are and how you want to do your maintenance. Your first step may be as simple as to create and mount the SYSPLEX root filesystem with your current member root filesystems mounted to it. It is recommended that SYSPLEX root is mounted RO. It think this makes sense. You can always mount a RDRW filesystem to a directory off of root. We will use the /global directory for this. For our shop, we keep SYSPLEX root and the member root systems as RO and mount additional RDRW filesystems as may be necessary. This way when we perform our maintenance, it is just a copy of the target zfs filesystem into another dataset and a replacement of the system dataset.