Game listenserver options and are there any downsides to use instead of dedicated?

Hello UE community! I have a few questions about starting a listenerver with the regular sort of options, but a couple in particular I couldn’t find a lot of info on ‘spectateonly’ and ports.

Does listenserver with spectateonly argument limit the entire server as a spectate server, as in a chatroom or similar, or is the executing listenserver joined as a spectator and all others as regular game clients? Are there any gotchas when using this to launch on a headless system?

Is it a requirement to specify the port (ex 7776) in the arguments, or is having the correct ports opened enough? (and what is the difference between using 7777 and 7776, I’ve seen both referenced.)

I’m almost done configuring my server and would like to see what these things mean to be ready once it is finished. THX!