Do you want to add numbers when importing the photos or afterwards?
When importing, use the "Rename Files" brick in the Import panel. You may have to add this brick from the "Import Settings" drop-down panel.
Then use one of the presets that will add an index or counter:
If the images have already been imported, try the "Metadata" menu: Metadata > Batch Change > "Custom name with index" or similar.
All these methods will change the version name in Aperture, but not the original filenames. If you actually want to change the filenames of the originals, try "Apply to original files" when batch changing the version names.