I WILL IGNORE REPLIES FROM NORMAL USERS. IF AN ADMIN RESPONDS THEN I'LL ANSWER.
Haven't been here for a while lol.
1. For the sake of performance of any server, and for QoL sakes, let us choose our server version instead of making us use ViaVersion/ViaRewind and all that. Also, I'd recommend letting use choose Paper or Tuinity. Tuinity is basically a fork of Paper (Paper itself runs very good, better then Spigot), that is designed for high player counts. It mainly has a bunch of chunk/entity rendering settings, that can greatly reduce TPS lag and CPU usage.
2. Plugins Updates and Requests:
1. SuperVanish and CS-CoreLib needs updating.
2. Add UltraPermissions, LiquidTanks, and HeadDatabase. Even though they're premium plugins, they're very high quality. https://www.spigotmc.org/resources/ultra-permissions.42678/
https://www.spigotmc.org/resources/liquid-tanks-1-8-1-15.18780/
https://www.spigotmc.org/resources/head-database.14280/
Slimefun Addon Requests:
The developer doesn't use Bukkit/Spigot anymore. They have their own Builds page which has all of these addons.
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/ChestTerminal/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/ColoredEnderChests/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/DyedBackpacks/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/ElectricSpawners/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/ExtraGear/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/ExtraHeads/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/HotbarPets/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/MobCapturer/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/PrivateStorage/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/SlimefunOreChunks/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/SlimyTreeTaps/master
https://thebusybiscuit.github.io/builds/TheBusyBiscuit/SoulJars/master
https://thebusybiscuit.github.io/builds/John000708/Barrels/master
https://thebusybiscuit.github.io/builds/J3fftw1/SlimeXpansion/master
https://thebusybiscuit.github.io/builds/J3fftw1/SoundMuffler/master
https://thebusybiscuit.github.io/builds/Sfiguz7/ExtraTools/master