One of the reasons I decided to start a business help authors self-publish their books is that there were so, so many people I talked to that had great ideas or partially completed manuscripts and I wanted to help them make their dreams a reality. There's nothing quite like the feeling of seeing a book with your name on it.
Writing a book can be daunting, but when you break down the work into manageable chunks, it's simply a matter of plodding steadily forward until it's done. After the outline is complete, I like to think of my books as simple "fill in the blank" forms. The hard work of writing is in the conceptualization and planning stages.
It's natural to wonder, while you are writing, how your book will be received. Defer these questions and concerns until the writing is done. It's also natural to worry about the cover art, interior design, and other technical aspects of book creation. Again, the time will come for you to face these issues, but set your concerns aside for now and just write.