The first problem I see is a typo in the ProgramArguments
key (you have an extra "m"). If fixing that doesn't make it work, I'd add something like:
<key>StandardOutPath</key> <string>/tmp/logstash.out</string> <key>StandardErrorPath</key> <string>/tmp/logstash.err</string>
...and see if those files tell you anything useful about what's going wrong.