Very nice set up. I would probably just code it to hook up to an Instagram content and scrape the images directly instead of going through Twitter though.
True, though from the article, it sounds like they first set up Twitter integration and then added on Instagram to that as an evolutionary step.
That's exactly how we went about it. We could do a full Instagram integration, but we never used IFTTT and it saved us some coding + kept the example codebase much simpler.
IFTTT does have downsides tho, very slow to push from Instagram to Twitter.