Since we can only fetch so many tweets a day, we should cache tweets locally. I would implement a configurable file cache (which we can set to our google drive folder), which saves tweets in a file named after the user's twitter handle. Before fetching, we should always check if this file exists and if it doesn't we will create it. I would implement the Serializable interface in the TwitterUser class and then use that to save and restore the instances.
Create classes to analyze reddit data much like we are doing with twitter data. Instead of fetching data from twitter, I would just read local files generated by your reddit fetcher. You could then extract the commonly usable classes from the twitter.stats package into a new stats package, and implement them in both the twitter.stats package and a new *reddit.stats package. Most code should be usable for both use cases. Coordinate changes with @christian176 and @DavidStei, as they are working on the twitter part.