Should I Upgrade My Google Apps Account?

I have a free Google Apps account, using an old domain name, and 7 users including the administrator are connected to it. Will I need to pay anything in order to:

  • change my domain name to a new domain
  • add more users to my account

And I believe I am getting 5GB of storage for free with Google Apps. If I upgrade my storage plan will I need to start paying $5/month per user too?
Any ideas? Maybe this is a better question for Google Apps support directly to be sure…