I'll add a couple things:

2. More than likely you'll want to back up your main into melee range of the following alts. There's no easy way really for this, unless you can control all 4 alts identically and have them in the same space -- /follow usually accomplishes this and stacks them on each other.

3. I have an addon to do just this but can't recall the name. However, multiboxer V2 does this and more and is quite the necessity for running multiple accounts. It will auto accept shared quests and auto complete turn ins, except if you have to choose a reward...also will auto accept questgiver quests as well.