If a thread has (Open) next to it, then you can jump right in. The one on Samora is also open, I just can't remember if it has that tag. You don't necessarily have to plan out a thread. For example, you could start a thread with Lortor walking in a park and then go from there as others jump in. The Planet Z thread that Glitch made does have a story arc involved, but only he knows what it is at the moment.
I do not believe the profile automatically fills in, unless one of the other staffers figured out how to do it. The purpose of the profile is so that everyone can just click once and see everything about your character. It's easier than hunting for your application. You don't have to fill it out right now, but we ask you do so relatively soon.
Ask us what you need to.