This is a good choice if you're just starting and don't have much money.
In the case of indie developers, few include racy themes or art as they are often trying to appeal a more family-friendly audience.
While it certainly helps - especially for gameplay - it's really not necessary to play original Japanese visual novels or dating sims.
Instead, having very good writing skills is far more important for both visual novels and dating sims (although a bit more important for the visual novels).
Writing skills also means coming up with original plot ideas and carefully planning each path.
In terms of the art style, it does seem that manga is the dominant art style for VNs.
As for theme/setting, anything goes: from dark sci-fi to cyberpunk, from historical to light comedy, like my latest dating sim "Roommates".
To be clear, they originated in Japan and, while many visual novels or dating sims are erotic (or at least sexy) in nature, it's not true that all dating sims have erotic content.
It's really a shame that people automatically label these games as "adult only" because, in many cases, is not true.
That is the shortest and smallest VN I've made.
Some of my upcoming games have 20 characters, each one with 5-6 expressions, animated eye, animated lips and three or four different outfits along with animated backgrounds.
That tool combines the powerful Python language with a full set of commands that lets you easily create a visual novel or dating sim.