Oooh!! Good luck to you fellow artistic writer! ^γ ‘ ^
I think it really depends. If you're planning to write a lot, you might be feeling pressured because not only do you have to write lots, but you have to draw lots with more script (character expressions, outfits, etc.) if you're planning to have more variation!
I personally like a good story, so I'm spending about a week on writing, a week on sprites, a little more than a week on CG's and GUI! :)
Also, just read your synopsis of your VN! It sounds really cute!! I can't wait to play it. :3