Hi Mike,
If/when the client responds via email, the update will get added to your ticket automatically (by the Mail Manager) in the form of a Note. This is why you need to place the logic after the Add Note action at whatever status you are monitoring. After that, you can have it do whatever you want it to... Add Reminder, etc.
You don't HAVE to use a Note to send out a Reminder... I do it that way because it allows the person to enter whatever they want, then I inject that text into a predefined format I've used to generate ALL reminders (by defining it on the Reminder object).
-Brian