RAID, OD, and network questions

I am planning to setup a home OD server and had a couple basic questions.
1 -
Would a safe setup for an OD server be to install the OS on drive A and then setup the users directory on RAID 5 system. My thinking on this is if the server OS ever has a problem I can do a format/install on drive A and not worry about data loss.
2-
If the above sounds like a good idea then I need to come up with a good RAID 5 setup. I do not want a RAID system that requires a PCI card, I would much rather have a Firewire or Ethernet.
I was thinking Drobo or Netgear ReadyNAS....but now I am looking into getting a cheap linux box with RAID 5, gigabit and a 5 bay storage. I will come down the to the cheapest box I can get (plus drives)
Anyone have any idea's on a good RAID 5 box?
3-
Now for the network part. I see it as follows:
1 Router
2 Gigabit switch into Router
3 NAS, server, and clients into switch
(If the RAID box is FW then it will hook up to the server directly)


Tell me what you think about this setup. I'm really looking forward to any idea you have about the RAID box

Thanks!