What do you mean all events?
The Topic you specified will send you all new followers as they occur for that to_id as long as the webhook is active/within lease time. And you continue to maintain the listener.
Correct, you set the lease time to whatever you want, the maximum is 10 days and you need to manually recreate the link. You will need to space out your reconnections to stay within the posted rate limits
No you cannot receive notifications about unfollows. This leads to harassment of the person unfollowing and as such is excluded as a notification.