My advice may or may not be helpful...
IMHO, it's simply not a good idea to put an OS partition in a software RAID. Unlike a hardware RAID, a software RAID will not give you the functionality of simply replacing a hard drive and "it works". It will complicate recovery efforts, if anything.
If you want to experiment with software RAID, I think it's more realistic to assume a scenario where the OS is in a normal partition while data is kept in RAID partitions.
My prefered method is to set up backup OS partitions on all of the hard drives. When I make major changes to the "live" OS partition, I copy the live OS partition to the backups. I have GRUB set up on each drive. Thus, in case of failure I can swap to a backup drive.
My method doesn't provide continuous uptime, so it's not suitable for a mission critical server that needs constant operation. IMHO, software RAID isn't the solution for those mission critical servers. If you need 100% uptime, you need hardware RAID and/or redundant clustering.