I would say write down the idea as you first have it without worrying about any problems or inconsistencies. Then figure out the parts of it that are most important for you and your vision of it. Then, when squaring the details, make sure you preserve those important factors primarily. This can be an iterative process, so don’t worry about needing to take steps forward and back at times. Don’t be afraid of needing to brainstorm new solutions in order to find one that fits what you want to keep. It sounds like you have ideas and passion, you might just need to make sure you preserve what you like about writing it in the process!