I think I saw all current content without error, so that's good. It appears the way to avoid content is to not take the quests or interact in the first place. In the case of the old man's quest, it's explicit what content you'll be getting, with the duke, you can guess it'll lead to voyeurism, but talking to the man spying on Lily, not so. It's obviously a minor thing, especially this scene in particular, but personally I'd like to know what I'm getting into.
How much will players be penalized for not doing quests in terms of material rewards (gold, the knife, etc.)? And will branching mean missing content of different type e.g will avoiding a monster sex quest potentially mean missing a vanilla, NTR, etc, scene?