I'll let some keyclone pros take care of the first 2 for you but to answer 3

Curse client can update any number of WoW folders even on different computers, you simply have to add games, select WoW for all of them and point it to the appropriate addons folder. After that it can update your addons and you will have a list of each "game" on the left hand side. I would be a bit more exact but if you have it set up for one you should be able to set it up to mangae any number of them, just pretend like you're setting it up for one everytime.