Something I remember the man who made the Fall from Heaven
Civ mod saying is that the best way to get the help with specialized skills you need for a collaborative amateur project is, paradoxically, by being willing to do everything yourself. Even if you blatantly can't do things you want to do to the required standard, the willingness to try, and the fact they're adding to something in a decent state of completion, assures people with specialist skills that their efforts aren't going to be wasted when everyone loses interest. Asking for an artist with a drafted or completed script in hand is more likely to get a response than saying "guys, I has a cool idea". Learning to draw manga-style characters, even to a shitty standard, and making the damn thing gives you a decent chance, or perhaps, or attracting someone with actual talent who likes the project to improve that aspect.
Besides which, if you seriously think decent art is necessary for a workable VN, 07th Expansion's sales numbers say you are somewhat wrong.