We will be able to become registered users of Pottermore later, so we will need usernames and passwords because it wouldn't work any other way. Or did I get your question wrong?
Yes. You dont choose them though, there are a list of I think 4 (lol I don't even remember for all I know it was 2) usernames selected at random in which you can choose from. Most of them sound really cool so don't worry you'll probably like it or grow to like it as you go along. I go by the name MidnightElm, trust me you'll like the names I had trouble deciding which one I liked more lol. :)
