order of files in a slideshow

Just be careful when you create a custom order: if you then go to a different order (say by date), your custom order is now toast and you'll have to recreate it from scratch. The only way to get back to a custom order (if that's important to you) is to rename all of the images. E.g., MyCustomImageOrder-001.jpg, MyCustomImageOrder-002.jpg, MyCustomImageOrder-003.jpg, etc.

I belive the slideshow follows what ever sort order you have in your Content Pane and it also starts on what ever photos is currently selected. If none are selected it starts on the first photo. There's a lot of different sort options, including by name and date. You can also sort your photos manually by dragging them in the order you want.