The problem with RAIDZ is resilver time. If you do the math on the time it takes to resilver, and view that against the chance you will have a second disk go bad (and thereby destroy your pool) you will see that it doesn't add up. The resilver time on an 8TB is way too long vs. the MTBF of the other 7 disks. RAIDZ is just not an option in practical terms.
So 1).
However, I do not have experience with super wide vdevs. I think they too have resilver time issues. So RAIDZ2 might not be a good idea either with something that wide. (EDIT: with some searching I think you can find a calculator online that will tell you if you are likely to hit problems just from an error rate / resilver time perspective. You plug in the drive capacity, number of drives and number of redundant drives and it lets you know the probability of failure.)
So while you can obviously ignore the advice, I still think you (most likely) need more disks for a reliable system at that level of data capacity. :)