Any media director (PC running the LinuxMCE software booted from the network), can independently access media stored at the core, or on the network.
This is by design.
Please read the wiki, a lot of the questions you are asking, have already been answered there.
Sorry, I'm a bit of a bone head I guess, but when you say "wiki", to what are you referring exactly? I read the user and installation guides and didn't see any reference to this. Is there somewhere else I need to look?
The other half of this question that I didn't express clearly enough is: Do I need any special hardware considerations to do this? For instance would I have to proportionally beef up the Core in relation to the number of TV's I might be using, etc?