Is it possible to make the checkbox of "Posting as anonymous?" selected by default to prevent user's identity from being disclosed accidentally if they forgot to select it?
One challenge: while posting anonymously, can you also let user to enter a nickname for each post?
Yes it's possible for them to behave like 2 or 3 different people in the same thread too if they want to. It's an anonymous thread anyway. On the good side, it's far easier to identity who's who by recognizing nicknames in the thread or across the threads in the same anonymous forum than an ID..