I don't know the pros/cons of RAIDing the whole drives and then partitioning, versus partitioning first and then RAIDing the individual groups of partitions.

There may be some decent rationale for doing the latter.
One reason to partition first, is that it allows using RAID1 (bootable!) for the operating system partition, and then RAID5 for everything else.

But I prefer a separate flash/SSD drive for the boot/OS.