Cavechan,
Looked over your first Chapter. I feel the artwork is looking good. When doing comics I always try to keep in mind each panel is one frame of artwork, so what is the best way to illustrate what needs to be communicated in that panel. Keep experimenting with different ways to communicate effectively and clearly with each panel, then also how the overall page flows as well (ex. is it easy to follow and makes the reader want to continue on to the next page. Also, I'm sure you are already doing it, but seeing how many kinds of comics set up their panels is good research too.
As for the story, personally, I would avoid going back to change things. Imagine that once something is published/ posted it's finished. You can't touch it anymore. Anything you might need to change, try to handle/ adapt for it in future chapters.
That said, I personally wouldn't work on any story that doesn't have a finished script. Writing things as you go can get difficult to manage the longer you draw out the story.
Hope that helps. Best of luck with the story!