Have you read the book?
If you have access to the book, Getting Things Done, you should give it a close read. There is a lot of great information in the forums too but it all makes more sense having read (and re-read) the book.
Your Next Actions list(s) should contain only those things that you are committed to doing that you can do right now. With reference to a specific project, you should have at least one Next Action but if you have more than one they must be independant. Any other planned actions that are dependant on finishing something else should be stored in Project Support.
I don't know anyone who has only one project. I currently have 43 work projects and 46 personal projects and about 150 in Someday/Maybe. My Next Action lists are split by "context", which defines which actions I can do at any given time: at home, at work, errands etc. David Allen suggests some default Contexts to get you started and I highly recommend using those for a while and then tweaking them to fit your work and life.
You will want a Waiting-For list as well to keep track of everything you are waiting for from others.