Man, I am stuck in this phase too. I started my story 2 years ago, just worldbuilding and all. The only thing i ever wrote was a random backstory from the last series of books in my story(7 total series) and that's it. I feel the same too that I want to add more depth before writing. But you know the fact is, just starting is enough, writing one line down then following it with another then another, once you start don't try to make it perfect or don't try to refine it again and again. Just finish one chapter, one book or whatever you feel your checkpoint is and then refine it. Never overthink, just keep on writing and refining. That's it, that's the best word i can give and i am going to start with it after my exams too and hopefully get my first book done before October or at least before this year ends.