aggiech, if you want generosity of spirit check LOTR's posts... He spends so much time helping people around here that I'm starting to think that he works for some kind of good-will organisation or something
Anyway, first what I say in step f) is to take a single file that would seem reeeeaaaal popular (dunno, some hip-hop song or something) and download that. If you did the bits-to-bytes conversion well enough, then that file (with enough sources) should be able to get you somewhere around that number. (actually, you may have to try with 2 simultaneous dlds, as your download bandwidth seems quite large).
Have you done a Bug Report test?
As for knowing if the combined speed is nearing your max bandwidth, AFAIK adding them up is fine. You have to know that the more files you dld, the less available bandwidth you will have, because aside from bandwidth used to actually dld the file, some is also used to send messages between the downloading user and the uploading user.
Help any?