It depends. Some successful manga artists can earn a lot of money through book sales, merchandise, and adaptations. But it also requires consistent hard work and having a hit series. Not all successful artists become extremely wealthy.
I think there might not be a direct connection. Hentai manga is a specific genre, and a rich heir is a character type. They don't typically have an obvious link.
The unique storyline and well-developed characters make it stand out. The contrast between the devil's supernatural powers and the urban setting creates an exciting plot.
A successful relationship in such a manga scenario often depends on the characters' growth and change. The poor guy could strive to improve his situation and the rich girl could learn to appreciate things beyond wealth. Their love could be the driving force for them to face challenges together.