Maybe Kyou kara Ma no Tsuku Jiyuugyou! ? It could fit 2) and 4), and has a BL undertone. A boy gets flushed down the toilet and finds himself as the unwilling demon king in another world (enemies: humans), and even got himself a jealous possessive husband by accident.

For the first one, Big Order maybe?

This is kinda spoilery, since the actual ambition is releaved quite late in the game but for the first one, Jormungand fits the bill.

I've only seen the anime, but by what I've heard, the manga and anime are pretty much identical. Until the reveal, her plans remain a secret to both the reader and all of her henchmen.

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