You can use AppleScript to do this if you fancy a bit of automation through scripting. Although there doesn't seem to be a specific scripting option to name the exported files numerically, the photos will get exported in the order that they were in on your camera, and they'll retain the same filenames too.
In Script Editor, create a new script and try this code out, adjusting the album name and export path accordingly:
tell application id "com.apple.photos"
set photos to every media item in the album named "Seville"
export the photos to "/Users/CK/Pictures/Seville"
In my case, the album "Seville" was a top-level album, and not one that was nested deep inside other folders. But Photos.app is pretty smart, and if the album name you provide is a unique name, then it doesn't matter where it is or how deep it's nested within a hierarchy, it will grab it for you. If there are two albums that share the same name, it will grab the top-most album by default, unless you specify exactly which one you're after, e.g.:
set photos to every media item in the album named "Camera 1" in ¬
the folder named "SwannView" in the folder named "London II"
Simple, right ?