WRT MiRai's comment about multiboxing basics: amen. I ran a 2-man group 1-80 (RaF) to work out those issues. Then I went to the 5-man teams.

WRT #3, i.e. the biggest difference between 2-man teams and 5-man teams; do not forget the hardware requirements. 5 instances of WoW require considerably more GPU and CPU than 2 instances.