> Some searchs talk about a separate /boot partition - I don't
> understand why that is needed or relevant.
>
> I'm assuming I'd make a mdadm v 1.2 raid 1 partition for root.
Your /boot must be in a regular partition or in a raid1 volume. It may either have it's own filesystem (I typically use one that's 512mb in size) or in the root filesystem. If it's in the root filesystem, then that means that root should be in a regular partition or in a raid1 volume.
I typically put /boot in raid1 then create a raid5/6 volume, then I create lvm volumes that use the raid5/6 volumes.