Idk, 12 is not too much imo. And you don't even have to add new characters. Just take existing once. Like Moon or Juliet for example. Hana. Kate. So many options.In case of harem building setup, I don't think "more is better" method always works, too many characters only make themselves less appeal, less noticeable, less attractive. I think the 8th room should be the last room in Hotel.