Did you used AJAX in your customer.aspx? You didn't mentioned that.
If yes, then you can just show/hide panels based on View/Edit/etc modes.
I think you can show the Records in Gridview & you can have buttons in Grid for Add/Edit/Delete/View for showing the details in another panel which contains also button for navigating to Record list. All you need is AJAX.
You can disable back button by below javascript.
<script type="text/javascript">history.forward();</script>
Please let me know if you have any doubt.