I would say realistically the Zephyr will be enough for a great many N and HO scale users out there and its one of the cheapest complete DCC...
Buy a book like that DCC guide (2nd edition) that the model railroader magazine folks put out or something so you know what you are buying parts...
Assuming you still are interested in what you were back at the beginning (I may have missed some posts) my best suggestion would be to pick a...