I don't see why 5zig would be disallowed. It gives little to none advantages over others. For example it allows you to add friends, copy coordinates to an in-game "clipboard" and chat with those friends once they have been added.
Damage Indicators is also fine since CubeCraft already has a "kinda" damage indication feature in most game modes (SCB, SkyWars, KitPvP, etc.).
And of course, OptiFine is allowed.