To clarify, you don't necessarily need a transforming search in your searchTemplate. However, note that if the searchTemplate is non-transforming, then you may or may not reach the 10,000 event search limit.
The real issue here is in the field extractions not being passed down to the post process search. All searches in dashboards are run in fast mode, which means that selected fields are not automatically available to downstream searches.
As a workaround, you can add "| fields *" to your searchTemplate to explicitly extract fields for post process searches.
If you have trouble with the way it's presented in the official docs, the Sideview Utils app has a more real-world approach for keeping you out of trouble. Download and install the Sideview Utils app from http://sideviewapps.com and navigate to "Key Techniques > Using PostProcess > Introduction". Far and away the biggest problem with postprocess is that everyone does exactly what you're doing here, and for several reasons, it is a bad idea and/or it will not work at all. The Sideview docs break it down into the different problems and pitfalls. In this case it's because the Total field is not named in your base search, so Splunkd wont even extract it at search time. The answer is as MuS says - to use a transforming command in the base search. But I do recommend reading the docs thoroughly AND reading the Sideview Utils docs as well.