Extracting fields from existing message field in windows logs

I suspect Most of this would be done for you with the pipelines if you just sent winlogbeat directly to elasticsearch .... if configured correctly... and you run setup etc.

I always recommend getting the Beats->Elasticsearch architecture working first before introducing Logastash

Once you get that working then you can move towards

Beats->Logstash->Elastcsearch Ingest Architecture

When you put logstash in the middle some important data is not forwarded unless you use the correctly

Here is a post on similar.. its filebeat but the concept is the same