Definitely get an authenticator. With battle.net, things seem to have gotten slightly easier for hackers due to the email link to your account.

I put all my accounts under a single battle.net. No real advantage, but I only need 1 authenticator. You simply go to the battle.net user config (or whatever it's called) and there is a command to add your non-battlenet wow accounts to the battle.net account.

Also, it's probably best to make sure you setup everything with ISBoxer before you even get your slave accounts going. This is simply due to the virtual configuration files etc. I don't use ISBoxer currently, but might switch in the future.