Overworld size is 40k x 40k.
Claims are enabled in the Nether and you are allowed to live on the roof if you know how to get there. There is no world border.
Claims are disabled in The End. Legacy players can ask one of the owners to claim some land, and this claim will be a world guarded region.
Resource world size is 5k x 5k. You can find the portal to Resource World directly ahead of you at /spawn. This is the only way to enter.
This dimension resets every 24 hours, so it is not advisable to build anything there.
Resource World is meant to be more challenging, so it's set to hard mode. You will find that it's always night, there is no health regen, you cannot run /back, and phantoms can spawn naturally there.
Most Slimefun had to be disabled in resource world. This was not intended to be the case, but it was very buggy and caused too many issues. Slimetinker weapons, tools, and armor do work there.