How do I increase the number of shortcuts allowed in admin menu?
The maximum number of shortcuts is defined in shortcut_max_slots(), which just returns a variable:

return variable_get('shortcut_max_slots', 7);


So all you need to do is change that variable to something larger than 7. You can use the devel variable editor to do it, or just run the following code from somewhere:

variable_set('shortcut_max_slots', 10);