How do I schedule different Leads to send emails on different date ?
When you want to schedule emails to go on pre-determined date for individual leads so that all leads won't be scheduled on single day.
How to stop sending off further messages other than Unsubscribe ?
Unsubscribe is not the option to stop sending emails. Stop Followup is the right option to stop sending emails.
Unsubscribe is used only when the end-user clicks unsubscribe or write ‘unsubscribe me’ (or something like that) in the email. Then Assistant will automatically unsubscribe the lead.
If the Assistant fails to read unsubscribe response for whatever reason, you can manually unsubscribe the lead if the lead requested it specifically. 99% of the time, you will never have to unsubscribe manually.