I would recommend things such as the following:
The guns plugin (music disks as guns etc)
Custom Texture (Preferably to make the disks look like guns)
Bleeding out
Faster zombies
Custom Spawning of mobs (make zombies spawn more frequently and with greater numbers)
Interesting and exploring worthy landscape
Custom generator plugin (massive city spawning at your command)
Loot chests in places such as hospitals and hangars with valuable supplies
Survivors hub for trading
and thats all I got hope your server works out
