If I understood things correctly: you can only be outside of a capital with 1 character at a time. That character would be considered your main while the character stationed in a capital city would br your alt (bank/disenchanter w/e)
I don't think so. The only time two characters are allowed to be online is when one is in a capital city for banking or profession purposes. Having one out in the world to camp a world boss and another out in the world actively being played is against the rules.
There are, however, ways to bypass the "multiboxing" accusations and having unlimited accounts online for a purpose like this. Won't explain how, as I'm sure that'd be considered as exploiting the ToU.