Your server is going to be a beast.
To have say 10 users all able to play streams idependantly, I think you may have to go for a fast HW RAID setup - FlexRAID etc would be fine if all your content were playing from different disks, but I fear you will have problems if several people try to stream media that resides on 1 of your disks.
As for network bandwidth - you will not need fibre. You will not even need Cat6, as Cat5e is more than capable (although I would also pull Cat6 if I was doing it nowadays). You just need a decent multiport NIC (Quad Intel Pro/1000 PT) and a good switch with a few more ports than you think you will ever need.
If you want to transcode 10 streams at once, you will also need one hell of a cpu. I'm afraid I don't know exactly, but I suspect you will need 2 4 or 6 core Xeons to handle that kind of thing, assuming of course that you need all 10 users to have a full transcode. I would only build 1 main box, then either use SAS expanders (kind of like network switches but for HDDs), or build slave boxes and tie them to your main box via iSCSI to save on cpu costs.
You do not need 6Gb/s controllers. No mechanical disk comes close to saturating a 3Gb/s interface, and no normal mechanical disks can even saturate a SATA 1.5Gb/s one yet. In any case, I suspect you need a HW RAID card anyway to support your usage requirements.
Regarding OS - WHS can only handle 32 drives IIRC. You will need to run a full server OS if you intend to use more disks than this.
One final thing - I would not consider protecting more than say 10 disks with a single parity disk, or more than 15-20 with 2. If you really expect to get up to 60 disks you will need several drives to hold the parity data even if you do go with FlexRAID.
Finally - where is the media now if you have 60 disks worth? If it is all still on the original optical disks, get ready for a LONG ripping session...