Just one question: if it goes wrong will the drive die beyond repair or is it recoverable to the current state?
Well you should allways be able to return to "factory defaults" by taking the drives out of the box (and the tray), put them into a PC and delete all partitions, and the rebuild drive 1, following the instruction given here: http://forum.buffalo.nas-central.org/viewtopic.php?f=22&t=3641
step 4-6 and 25-40.
You are making your box ready for firmware update so to speak, and in step 39 you firmware update your box.
(You can go this way to firmware update you box as a "Plan B")
This goes if you do not fail with updating of the internal flash memory, this can happen in case of power failure during update.
It can be fixed, but I think it is out of your scope, JTAG is the keyword for this.
But if you use an UPS, or your power supply is stable and normally without dropouts, I do not see any reason not to try to firmwareupdate.
If you live in my place, you do need an UPS for your PCs and accessory, so I do have 3, yes, power-failure often in this part of town.
BTW, with a 8TB box you will be needing a lot of coffee, formatting of 8TB takes time, re-sync of 8TB takes time.
Expect hours, many, I recall my test to take more than 12 hours for the re-sync.
Re-sync is not at failure the first time you see it, it is a process you have to do.
The re-sync time may depend on your RAID level, mine was RAID1.