Welcome. :) While it's always good to push your limits, I think that you're probably a couple thousand years late to write something no one has ever read/played before. But, as they say, it's the journey that counts more than the destination. Just keep that goal fired up. And yes, it is wise to start on a smaller project. There's a bit of a mental readjustment involved in writing a CYOA style story. I jumped into a contest without writing a story first and I struggled quite a bit with it, despite the fact that I've been writing linear stories for at least 20 years.