Expenses Notification

I there are 2 requirements to set up the notifications. how can this be achieved.

Employee submitting the expense report should get notification one -

1. New transaciton created
2. Weekly reminders for transactions pending to be tagged to expense reports
3. Weekly reminders for expense reports not submitted

Approver-

1. Expiration of approval request in 3 week
2. Escalation-to manager after 3 weeks
3. Escalation-to dept head/HR after 45 days