Two nights in Nikko seems like a very strange choice. Four nights in Osaka vs. only two in Tokyo also seems odd.

One night in Osaka, two in Kyoto and five in Tokyo seems like a better balance if you consider how much there is to see in each location (skipping Hiroshima and Nikko altogether). However, Kyoto is pretty boring at night, so you might want to reverse the Osaka and Kyoto ratios.