Regarding "global sheet", I'd suspect the meaning is the global VI expanded to full screen (or whatever is considered an allowable maximum size) now still requires scroll bars to see the collection of variables.
As to moving to a second global VI, you can certainly do that, but I wouldn't expect there are any built-in tools to help you.
A better option (given the likelyhood of manual intervention) is to check that you really need so many global variables. Could you consider changing your architecture to use more direct data-passing methods (value, notifier, queue, refnum as needed, etc?)
Obviously this depends on your code, and to a certain extent your target (globals seem to be more common on FPGA, for example) but it might simplify managing your code (and particularly aid in any future changes, especially with careful use of typedefs, etc).