Of course Luffy did not have enough allies already,so lets add Kizaru,why not 😒
You are not getting this right.
Kizaru won't ally with Luffy for the sole purpose of him being Nika.
Kizaru doesn't give a fuck about Nika. He didn't dance because he suddenly admires Nika. He did the Nika dance because he was with his friends who admire and idolize Nika (Kuma basically).
Kizaru cares about his friends who are Vegapunk, Kuma, Bonney and Sentomaru.
Kizaru is conflicted because he has a mission that is dealt by the devil (Saturn) but this mission involves hurting his friends. He still went after his mission but this hurts him inside. Kizaru is in shackles and his soul is trapped by Saturn. He is a cog in the machine as a consequence.
Nika defeating Saturn will liberate Kizaru from this conflict and he may switch sides to protect and ally with Vegapunk, Kuma, Bonney and Sentomaru. They may be part of "Luffy's grand fleet" but that is completely irrelevant.