You can't copy stuff from other plots to other nodes using World Edit, what you can do is, claim a plot in the same node as your friend's plot. Then use WorldEdit to copy it to your plot. Now you can use /plot clone to clone it to any plot you own in the main server regardless of the node
Oh yeah, and to claim a plot in the same node, you have to keep trying claiming plots, if the newly claimed plot isn't on the same node, you can do /plot unclaim to unclaim it and then you can try claiming again