Thanks Mike,
That got me there in the end.
Adding the Java option got the log4j plugin working. The following command started Logstash and created logs:
logstash -f config\logstash.conf --path.logs /E:/ElasticStack/Logstash/logs/ --config.reload.automatic
I couldn't get logging working for the service, however it turned out I had the LS_SETTINGS_DIR environment variable set incorrectly. I had read INFO: Windows, Logstash and could not find log4j2 configuration which suggested using the unix style for the path. I changed it to a Windows style and it picked up the logstash.yml config.
The configuration setting I used in the yml file was:
path.logs: "//E://ElasticStack//Logstash//logs"
Thanks for your help with this.
Tim