Does my email need to match the email in Strava or Garmin or other services?
The email address you use with Challenge Hound can be any email you wish. It is NOT related to emails used with any apps that connect with Challenge Hound. For example, you can sign up with email@example.com email address and then use firstname.lastname@example.org to login to Strava or Garmin. In this example, Challenge Hound will send activity updates to email@example.com and nothing to the gmail address. Challenge Hound will not even store the gmail address. It is just used to connect to Strava.
Challenge Hound emails are completely independent of emails used by third-party apps, such as Strava, Garmin, Fitbit, Coros, or UACF.