We're in the pre-production phase, so let's talk about your VN's scope! What's it about, and how big do you intend it to be?  

Writing
If your VN has a branching storyline, start outlining your story tree. How many scenes do you have to write in total? Is there a visible way on your tree to get to each of the endings? Are there choices or branches that don't seem to lead anywhere? Time to start pruning! What's your wordcount goal? How many words per day will you have to write to hit that?  Now imagine you only have half as many days instead. That's your actual daily word count.

Assets
How many sprites, CGs, backgrounds, or other images, will it have? What are your plans for sound? Will you be adding any extra features? Make a list of the ones you absolutely need to make the VN function, and prioritize those.

Time Management
How much time do you have to spend on these items? What about your team members? Be sure to agree on clear deadlines for the assets ahead of time.  Factor in weekends, and life events when you build your schedule.