Is it possible to reset all the data I have ever stored in my Health app, so when I set up my new Apple Watch I start from scratch? (all the challenges, rings, history of activity, etc.)
When I have set my current watch up as new (unpaired and re-paired) my health data was all erased from the Activity app. You can also go to the Health app, go to sources, and erase all data from your old watch so it doesn't show up in the Health app either.