travelling for 28 days

Hi,

I will be travelling from Sydney to Japan (Osaka) on December 11th.

We will be in Osaka from the 11th to 22nd December. We will see things like : Kobe, Bamboo Forrest, Aquarium, Temples in kyoto and Hiroshima.

From the 22nd December to the 26th December we will be making our way to Sapporo (Niseko) for the snow.

From the 26th to the 7th Jan we will be travelling from Sapporo to Tokyo.

We have already priced flights for Osaka to Sapporo and Sapporo to Tokyo for $560 for 2 adults.

Would it be cheaper to get JR pass instead of flights and if so what passes should we look into getting for the 28 days.

Thank you :)