I don't believe it will be sufficient to have the attribution of your icons only in the file's metadata (however, don't strip is out if there is licensing information in the metadata). However, I also believe it is not needed to break your design by adding attribution notices right next to each icon.
For the placement of attribution notices, it is best to differentiate between content and design elements.
For content (what is also shown in the examples in the Creative Commons FAQ), I would recommend to put the attribution right next to the third-party work (photo, image, whatever) as that is where people expect to see it.
For design elements, I would recommend to put all the attributions on a separate page. This is usually the same page where you would mention the third-party software that you used and the licenses that are applicable to the software. For the style of attribution, use the recommendations from Creative Commons.