There are lots of plugins that would be useful on a Skyfactory 3 server, including an essentials, permissions, protection, and island management plugin. Here’s some suggestions based on what I have seen people running similar servers use.
Essentials: Nucleus by dualspiral
Permissions: LuckPerms by Luck
Island Management/Protection: SkyClaims by Mohron which relies on GriefPrevention by blood.