The best suggestion really is to scale each item as you go unfortunately. You can change the size of items in groups by using the groups function just above the size, rotation and movement functions, selecting a group and resizing all of the items in that group in one go. Those groups do include an “All Items” group, but group resizing is an unreliable way to do it. If you have any items flipped it can set them back to their standard rotation and if you have any items masked to an item in a different group it can be quite difficult to find them again afterwards. As for All Items group resizing, it’s quite difficult to control the scale when resizing and it does have a tendancy to come undone during export or if you save and come back to it later. So yeah, best suggestion is to just resize as you go.