Generally the gdd looks good, but theme interpretation of the game is a little light in my opinion
The gdd is also more of a roadmap than a document of what you have now. You don't have to mention you don't have something implemented yet. It helps you plan and remember what you want to develop into the game and can be shown to others if you want to show off what you're creating
The development timeline's contents are great, but the the pacing is too short. You're going to be spending a lot more time to make it a finished product. Besides the time to implement everything, you will stumble upon roadblocks that will take you many hours to solve, even on a simple issue sometimes, so depending on the size of the final game and especially if you're not working on the game full-time (6 hours a day or more), set the development timeline to at least half a year.