Barnes and Noble often stocks manga, but it's best to check their website or call your local store to see exactly what's in stock. They might have a dedicated section for manga with a decent range of genres and titles.
It's hard to say when the Barnes and Noble manga sale occurs. Sometimes it's announced on their social media or in-store flyers. Keep an eye out for those!
In Barnes and Noble, light novels aren't regarded as manga. Light novels have a different style and structure, often featuring longer written sections and a different narrative approach compared to the visual storytelling of manga.