The design is decent.
The halloween-theme is not bad and I actually like it. Only complain is, that the cobwebs are a bit much tho. Maybe reduce it a bit.
Maybe add some eastereggs, for people that actively explore the spawn?
You could also add some armorstands, to make it a bit more "alive".
Good and decent use of holograms,.
Why blocking /help? Instead of blocking it, you could easly override and customize it.
You should reduce the clear-message. It shouldn't appear 3 times in chat.
/[tab] is blocked and /pl only shows custom stuff. That's good.
I tested the custom island. Looks decent.
You should try to reduce/disable the crate-message, when someone finds a crate,,, The spam is annoying.
Island plugin works nice and the addition of the custom ore generator is also not bad.
Yet it is still SkyBlock, so there is honestly not that much you could make wrong.
Tablist is ok. It isn't overloaded with unwanted information.
Final Rating: 8/10 [Really good]
This isn't directly server-related, but more a thing you should change at yourself.