a.) How often the user has plagiarized (and the last copied and pasted post)
There is no feasible way to detect that.
Oh, I said that because a large %age of the highly ranked member that gets banned were for post made as further back as 3-4 years,
Highly subjective and would just devolve into massive flame wars.
Yes, but that'd be up to the delegates to decide. I'm sure that regardless of how irrational a reputable member's opinion could be, they'all are against serial-plagiarist/spammers and it shouldn't be too hard to detect when one is found, considering how the plagiarists thread get busted with their copied post almost instantly after they create a thread to the know why they got banned.