As the title suggests, where is it that you can assign logstash a port? I've noticed that in filebeat, winlogbeat and so on there is an output section with logstash default to 5044, but is that the only place that offers a specific port for logstash to operate?
I'm not sure what you're asking. Many Logstash input plugins can listen to events on TCP and/or UDP ports. Which port to listen to is configured per plugin. Using port 5044 for the beats input seems to be some kind of convention but you can use any free port.