I think there is a huge difference between an illustrated novel and a graphic novel. An illustrated novel is a novel that can stand on its own but to which the publisher of a particular edition has chosen to add pictures. There are various editions of Lord of the Rings, for instance, both illustrated and not illustrated.
A graphic novel, on the other hand, is a long comic book. The pictures are integral to the work, not an optional addition.
The picture book, for children, is a bit of a hybrid. Most, at least, are written like an illustrated novel, so that the text can stand alone, but there are definitely some where there are additional things going on in the pictures that are not mentioned in the text. This style seems to suit the highly interactive nature of reading to a child, and the progressive level of comprehension that a developing child brings to a favorite book over time. I'm not sure this model is readily transferable to adult readers.
What you are proposing sounds more like an illustrated novel than a graphic novel, so I think it would be safest to write it as a novel that can stand alone and then to illustrate it afterwards. Don't make the text rely on the illustrations, in other words.
But I would also note that the description of faces in prose is relatively rare, since a prose description can only give the most basic caricature of a face (long nose, deep-set eyes, etc.). Most descriptions of characters physical appearance tend more to the figurative. And in most cases, it simply does not matter beyond basic characteristics like the heroine is beautiful and the hero is tall.