Honestly? The harem wouldn't harm the story with how it's been structured so far. If the main girl ain't Tsunade, you'd need a different cover. And if Harem: Tsunade, Shizune, Ino and Tenten would be the most likely members.
you could make him receive a summoning jutsu from your top secret clan, which would summon some kind of divine cat, it would be a good pet and comic relief just like Kakashi's dogs
