Hey. Thanks for the info.
Just in case you are interested: For this kind of games I always prefer to use twine. Is an amazing stand alone and online tool, specifically designed for this. I truly recommend you to try it if you are interested in the genre.
For design flow charts I use to work almost always with Google Draw, which can be embed directly into Docs online. This means that you can create your GDD almost enterely with only one tool. (You can always call spreadsheets from sheets).
Hope this is usefull for you
See you here in future!