The campaign design articles on the Wizards site are pretty good for laying this stuff out. That series is worth checking out. You can see there where the designer lays out lots of cool ideas that he wants to go with
eventually -- then draws back and figures out one solid starting town and dungeon, and focuses on that. The idea being that there's no need to develop too far ahead, since you'll want to see how things play out and what elements of your campaign the players really dig on.
So yeah, writing your own campaign is significantly more work than "one town, one dungeon" -- but that's all you need to start having a good time.
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