I just bought a Mac Pro and plan to set up a 4-disk strip RAID set for performance while making sure that all my data are safe. I have an SSD for system software and five hard drives for data. They are:
- Two Seagate Barracuda 7200.11 1.5 TB
- Two Hitachi Deskstar 1.0 TB (Model HDS721010KLA330)
- One Western Digital 2.0 TB WD20EADS (Caviar Green Power series)
The Seagate and the Hitachi are 7200 rpm. I don't know the rpm of the WD 2 TB drive.

I learned that in a Raid set all disks should be the same size. How about brand name? Do I have to use the same brand disks to do Raid 0? My plan is to partition the disks to get "same size". One of the setup I am thinking about is the following:
- Partition the 2TB Western Digital to 250GB/1750GB. Lets call the partitions R1 (250GB), Data1 (1750GB)
- Partition the two 1.5TB Seagate disks to 250GB/1250GB, call them R2 (250GB), R3 (250GB), Data2 (1250GB) and Data3 (1250GB)
- Partition one of the 1TB Hitachi to 250GB/750GB, call them R4 (250GB), Data4 (750GB)
- Connect the remaining 1TB Hitachi to the extra SATA port on the matherboard of the Mac Pro, call it Data5 (or connected it with an external firewire box)

Then:
- Setup R1, R2, R3, and R4 to a strip RAID of 1TB capacity, call it R, and put my regular working data (mostly video files) on it.
- Backup data on R to Data1 with Time machine (large capacity to store histories)
- Backup data on R to the external Data5 with Carbon Copy Cloner (both disks are 1TB capacity) every night, so I have two backups of my regular working files
- Put my "backyard data" on Data2. I don't work on these data. Whenever I need them, I copy them to disk R (my working disk).
- Backup Data2 to Data3 with the Cloner every time I move data to and/or from R
Well, Data4 is kind of wasted. My current total data is about 1.4TB.

My question:

1) If the Seagate disk (partitioned to R2/Data2) is damaged, meaning that the Raid disk R is damaged, do I still have access to the Time Machine backup on Data1? And the data on Data3, the backup of Data2?
2) How do I understand the performance of such setup? Supposedly the Hitachi is the slowest disk, so my Raid disk R is four times faster than the Hitachi disk? Do I gain better performance if I setup the Raid on the two Seagate disks and the two Hitachi disks?
3) Is Apple's built-in Raid software in the Disk Utilities reliable on this type of setup? Or I should go for a third party software such as SoftRAID? Or I have to go for a hardware RAID card?
4) Is this setup compatible with Boot Camp?

Any advice is highly appreciated. Thanks much.