Just to comment on iSCSI a hair.
I have a client for which I set up an openFIler iSCSI box. The box connects to an unmanaged dumb GigE switch. Four iMacs connect to the same switch. Client uses FinalCut to access video assets on two MicroNet 4TB external storage enclosures. Each of the four iMacs accesses two drives in the enclosures configured as a 1.8TB volume.
Been running fine for, I dunno, two years? Box blew a power supply this past month, I grabbed a second box of similar make and model, reinstalled openFiler, attached the enclosures, ran a script someone on the Net created to reload the volumes, and reconfigured the iSCSI. Back in business in a couple hours..
openFiler is great, utterly reliable, In this case, running over the client's regular network has been no problem, since the path is box->switch->clients all on the same switch and his network doesn't really move that much stuff around in normal use since the twenty machines are mostly production machines.
I'm thinking of setting up an openFiler based backup server for the video department - in that case, I'll use a separate GigE network based on separate NICs and a separate GigE switch - although I'm not sure what I'll do about the iMacs (GigE USB, I guess, if there are drivers - someone on the Net has done it). The rest of the department is tower Windows PCs.