ok, then let me tell you my config right now for 2 systems:
core and hybrid - 2.4Ghz P4 with 1GB ram - i have some barebones from msi
fast hdd - i think it's a 7.200 not a 10.000
as for media directors - again barebones, and some P4 from 1.8 to 2.4Ghz with 512 and 1GB ram
i think your config will be ok, of course you don't need to invest in a high end server, just get the best config as a core/hybrid with a god hdd, and the rest as media directors
Dan