An incremental strategy for large amounts of storage

Along with the PE1950s, I've picked up a PowerEdge 2950. This is a 2U machine with 6 drive bays. The current situation with a pair of 500 Gibyte drives mirrored leaves a bit to be desired in terms of available room. So here's a plan to get to ~12Tibytes of usable space:

• Acquire a pair of 3Gibyte SATA drives, ideally from different manufacturers.
• Do an OS install as before, with a mirrored 1Gibyte /boot and a mirrored 1Gibyte / filesystem.
• Create a third partition on each drive covering approximately 80% of remaining space. (The drives are being purchased piecemeal and will not all have exactly the same sector counts.)
• Get backups running -- there will be a period here where a one disk failure will erase everything.
• Using third partition on these drives, create a three disk MD RAID5 with a missing member. This device should have about 4.8Tibytes of usable space.
• Acquire third drive, extend mirrors of /boot and / onto it. (2 disk RAID1 becomes a 3 disk RAID1.) Create third partition of size greater or equal to size of existing RAID5 members. Add to RAID 5 array.
• Enjoy protection against single disk failures. But continue doing backups.
• Acquire fourth drive. Partition as above. Re-shape RAID5 into RAID6. Reshape 3 member RAID1 arrays into 4 member RAID1 arrays.
• Enjoy protection against two disk failures. Continue doing backups.
• Acquire fifth drive. Partition as above. Re-shape 4 member RAID6 array into 5 member RAID6 array.
• Enjoy increased space.
• Acquire sixth drive. Partition as above. Re-shape 5 member RAID6 array into 6 member RAID6 array. Reshape 5 member RAID1 arrays into 6 member RAID1 arrays.
• Enjoy increased space. Continue doing backups.
• Fail all array members on a single physical disk.
• Repartition disk, growing MD member partition to end of disk.
• Add re-partitioned disks's MD member partitions back into RAIDs they came from. Allow array resynchronization to complete.
• Repeat process for additional physical disks.
• mdadm --grow --size=max to grow the finished array to its maximum size (as determined by size of member partitions. Should be really close to 12Tibytes.)
• Continue doing backups. Collect large amounts of pr0n.