BIS,
a linux box won't help you since it doesn't know how to communicate over a processor link. there's a special protocol involved, it is not documented and is not available outside of avaya, or at least i don't know how to obtain such documentation. so if you add a processor link to a generic computer you won't have any results, a link won't be established and that's all.
cms network traffic depends on the size of your call center of course. i can't give you any numbers but you can set up a sniffer or port mirroring on the switch to log pbx-cms traffic. log it for a week and then count how much it is.
sorry, i don't think this is of any help but i think you really are trying to dig too deep. there are many simpler solutions available, no need to go into complications.