I would NEVER pull disks out of a functioning NAS box unless I had a full backup somewhere nearby.
I strongly suspect you can pull the disks and directly insert. You will encounter a feature called “Raid Roaming”, that will let you migrate the disks. Do some searches on that term. . . hopefully someone smarter than I can weigh in.
I am guessing your HDD’s inside the EX2 are not young. What I would do (Since I have more money than sense) is to buy new NAS with disks; and simply do a drag-n-drop copy.
For a new unit. . .I would likely choose JBOD over RAID. . .since I backup the data off unit-anyway.
OS/5 is not that great TBH. A backstep in a number of regards. For a new NAS, I would be inclined to not have WD on the shopping list.