There are several dedicated BL manga websites. For example, Mangago and Kissmanga have a decent selection. But be careful as some of these sites might not be legal or safe.
Echii mangas usually have more adult-oriented content like sexual themes and imagery compared to regular mangas which may focus on a wider range of genres and themes.
Schoolgirl hentai mangas usually have more adult and explicit content compared to regular mangas. Regular mangas focus on a wider range of themes and are suitable for a broader audience.
Hentai lolis mangas typically contain inappropriate and potentially illegal content involving underage characters in sexual situations, while regular mangas focus on various genres and themes without such explicit and objectionable content.
Yes, mangas can be considered graphic novels. They share many characteristics such as being a combination of text and illustrations to tell a story. Manga typically has its own unique art styles and narrative structures, but like graphic novels, it uses sequential art to convey a plot, develop characters, and create a fictional world.