Now is the time to make any final tweaks to address such concerns. Then give yourself a pat on the back for capturing this story just right.
The work you've done to articulate your book's value, purpose, audience, and competition is the keystone upon which your book proposal (and ultimately your book) will be written. By taking the time to slowly flesh out your book blurb and supporting points through the course of this year, you've had a chance to refine your vision and your story along the way -- both based on reader feedback and your evolving understanding of your project.
With your blurb polished to a high shine, you're ready to take the next step. Find your favorite how-to-write a proposal book (I used Elizabeth Lyons' Nonfiction Book Proposals Anybody can Write) and dive in. I expect you'll find that the in-depth preparation you've already done will serve you very well when writing the proposal. You'll be starting from an informed, confident place that is fortified with your best writing about your most passionate topic. There is simply no more auspicious way to approach agents and publishers and then bring your book into the world.
To your book's success!