Since NPE stands for New Player Experience, the question you should ask yourself when setting rules for it is always "would a new player do that?"
Examples:
Would a new player choose a unique name for his/her account? Most likely.
Would a new player trade/talk? Yes, unless he's completely anti-social.
Would a new player use items from his main account? No, because he wouldn't have one.
And so on, and so forth...