Quark has configs for this. That's what it was designed for. Another mod is not necessary
I think you have to archive it, then delete it.
Any idea what the weapons and drops would be?
...A mod isn't really something that can do this...
allow-flying is already an option in server.properties
Done. Is this satisfactory?
It won't work. Clientside authentication never does. Someone will make a modified version that always allows you to join.