Gunma-Niigata-Tokyo 2-weeks Itinerary

Hi there,

Am currently planning my year-end trip (in December) to Tokyo and am thinking of the following itinerary:
- Day 1: Tokyo (Narita) to Omiya - Day 2: Omiya to Kawagoe to Takasaki - Day 3: Takasaki to Echigo-Yuzawa - Day 4-6 : Gala Yuzawa
- Day 7: Echigo-Yuzawa to Niigata (Yahiko Shrine) - Day 8: Niigata Station (Sado Island) - Day 9: Niigata to Kusatsu Onsen - Day 10: Kusatsu Onsen to Tokyo - Day 11-14: Tokyo (depart from Narita)

Questions: 1) how does my itinerary look and am I missing out stop? 2) I am thinking of JR East Pass (5 day Flexi-pass) - which days should I use this pass to maximize the value?