Well I won't completely agree with above plan because its a shared storage. If array firmware is going to cause an impact, it will impact both the nodes as its a shared storage.
I would suggest to check with Vendor, if its an outage change, get a complete shutdown of environment, upgrade firmware & then start up both the nodes.
If you are using IOFencing, make sure that array firmware upgrade is not touching IOFencing keys on coordinator & data disks. If its a graceful shutdown of cluster it wouldn't impact IOfencing because, with shutdown of environment, keys will be removed from data disks & once array firmware is upgraded & IOFencing starts, keys will be registered again.
Also, firmware upgrade will enable the ALUA mode however make sure the array settings set it to A/PF-LSI mode
G