AnswerHub is a customer service 'BugTracker" website used by Epic to track bugs and answer questions, there is no reason you can’t use your same username/password over there. The forums here are a community resource where we can help each other with questions on how to do something, but there is no guarantee Epic staff will answer a question here (although they usually will as well). When you create a new on AnswerHub, it is assigned a ticket # and get’s tracked to completion, is the reason bug reports should be sent there.
There are no other websites you need to create an account for. I’ll leave it up to you, but I highly recommend that you use AnswerHub for issues like crashes or tools not working correctly, if Epic isn’t informed about issues it is possible they may not be fixed in a timely manner.