How to set up a spawn
You can set up a spawn either in the AcidIsland world or in a separate world.
AcidIsland World Spawn
If you do this, make sure you use bedrock throughout the island. The new island routine checks for bedrock and if it is not there it might place an island on top of spawn. Alternatively, you may want to make it floating in the air high above the sea.
Other world spawn
The advantage is that it is fully separate from the islands and can never be reached, or breached by plays in boats. On the other hand, you may want this to be possible!