You know i am not going to go through all of this trouble just to play on a simple game, I am not going to play on a server that has you have to jump through 10 different steps just to simply play on the server, run the risk of you getting trolled on it and loosing a lot of progress, then most likely no one have anything done about it. It shouldnt take this many steps to play on a server that says PUBLIC in the server listings on the server website. Ill be sure to tell my friends and other starbound players to avoid this server as well due to it requiring a crazy amount of steps to play a simple game on it.
On rare occasions, the server disallows anonymous connections when there are attackers joining anonymously.
This might have been what you experienced with the "we are not currently allowing guests."
Normally, you don't need anything beyond the IP and port to connect and play.
Exceptions to this would be, roleplaying on the monitored hub or entering the player build world.
These two hubs do require accounts to be able to enter.
Everything else on server does not require an account.
If you are still unable to join after doing the following, then odds are the problem lies elsewhere.
I have attached some images to this post on the matter.