This plugin adds a meta box to the coupon edit screen where you can make your own customized coupon message.
Yes you can. Just make sure that your HTML is correct, otherwise things may look strange.
If you'd like to use your own CSS style for the custom coupon message container, just enter your name of the CSS class in this textfield. You do not need to enter the dot(.) indicating that this is a CSS class. Only one CSS class can be entered.
No, this will not work, sorry. If you do this the default Woocommerce style will be applied.
Yes, they should, but in Internet Explorer 8 and below they look just ok (No rounded corners, shadows etc).
The plugin should work fine using all newer versions of Woocommerce (tested with version 1.6.6 and 2.0.5) If it's not working just ask for help in the support forum, and I'll try to sort out any bugs.
I might if I have the time. Let me know and I'll see if it's doable :)