2) How do I use formations; specifically, how can I get my characters to go into a straight line? This would be nothing short of excellent. Now,

"Now, what is A, or u, in terms of using a macro? In the "Basics" section above, it says that "multibox formations are not achieved through macros, they are only possible through key-bindings and key-mappings." What is a key binding, or a key mapping? I have no idea about any of this."

Key bindings are the simple act of going into the WoW menu and making the same key a different direction on each characters. Key mapping is more like making Keyclone do the different directions (making A on the main press B,C,D etc on the alts)

For a straight line I would think that setting 1 clone to forward, 1 clone to backward and the main as nothing. Press and hold, the 2 clones will spread ahead and behind the main theortetically in a line.
"3) How viable would you say more unusual combinations are, like 3 warriors or 3 rogues? Do you believe they can stand up in PvP?"

Melee setups are very hard. They all have to be in range, melee attacks cancel follow and no heals.