Hey!
I’ve seen many stories with realistic BGs and I would say that it depends how it looks like. Some of them just look like they are not from the same words as your Episode characters because they are too realistic. I’d prefer to use cartoonish BGs for Episode stories because they fits more with the characters. But again, you can still use realistic BGs but I think it should fit a little bit with the chars if you see what I mean…
I use realistic BGs too but not too much, when I use them, mostly they are BGs like a forest, the sky, BGs about nature/the environnement, maybe the streets too!