Do I need 2 Charging Docks and 4 Trackers?

No. One set (1 Charging Dock and 2 Trackers, one for each hand) is all you need for boxing workouts with full punch tracking.

To add kicks to your training, you'll need a second set, for a total of 2 Charging Docks and 4 Trackers, so you can wear Trackers on both hands and both feet.