Easiest way to do this is to go to the Image Manager (in the online section) and then the deletion tool. Once you scroll to the bottom of the list (you can press up to get there quicker) look for an image in the 900 range. Whatever the highest number you have is where you're at and the MAX is 1000 images. So if you're last piece shows 972, you'd have 28 images left you can download.
So basically what you are seeing/stating is correct. I've basically learned that the max CAWs I can have is around 70 (which is still nice) and a few custom Areans before I hit my MAX. Deleting/not using custom renders will help clear up space as well.
