I would like to retrieve the followers of a specific username such as "@justinbieber". Since he has over 70 million followers how many can I retrieve information from them? I only need their userIds.
We do not support, nor to the best of our knowledge does Twitter allow, the harvesting of followers from an account. Even if Twitter did support it, we do not handle so-called big data. Our optimal datasets are 1,000-1,000,000 items. Tens of millions would break our tools and cost more than the license fee supports.
However, once you have a list of followers and/or those following, you can set up additional rules to pull in tweets from those users. Unfortunately, the payload for these users does not come through with the original tweets they are following / replied to / etc.