We're in a similar position; We wanted to encourage our team to walk more during May, and got 300~ people signed up with Strava and joining our club. Our goal was to provide some prizes for 'groups' of our teams (Based on their office locations)
However, we've immediatly found that team-members are adding all sorts of activities and as we're unable to list data for the whole group broken down by activity I thought i'd try the API.
Nope - not viable.
1. Can't filter or obtain date of activity on club API
2. The lack of Activity ID means I cant get that extra context even with more API calls
3. The regular data exports only include top 100 members, missing 2/3rds of our group