There is not a guide for this type of setup. Both of the ideas that you have proposed would work well though. Another variation on these would be to have a single page with single UE server behavior but have the switch statement or other logic directly in the body of the message. This would give you the smallest number of files and least amount of code. If you goal is to make it easy to update the messaging then having the success page in multiple languages each with their own UE on them would be best.