Jim,
The "Send Email" Flow activity will only pick up an address that is in the default, non-custom "Email" field. So if you're adding a custom field that specifies another email address, it won't actually send to the custom field address.
As far as the 8 test emails (7 working correctly and 1 going to spam/trash), that could be as simple an issue as your spam filter assuming that multiple emails from the same address with the exact same content (or very similar) are spam. Check your spam filter settings to be sure.