Welcome to the forum.
Before going on, have you already purchased the
DS220j and if not can you stretch you budget to one of the more expensive DS 2-bay NAS? While the DS220j is perfectly good as a traditional NAS and running some of the headless open source server software it will struggle with the newer web portal and media handling services.
Probably not what you want to hear but if streaming is going to be important then you may end up buying twice: I did and have a DS215j and
DS218+, of which the latter was purchased to improve performance of Video Station, Moments, and Mail Server.
If you have purchased the DS220j then, provided you video files are in the right format (the DS220j won't be able to transcode in real time), then you can still run the media packages but the CPU will mostly be running high. For example, I recently installed Plex on the DS215j to see if it could stream a MKV from Blu-ray to Plex app on Mac. Streaming worked once Plex server had finished tagging but stuttered during tagging and the CPU ran at ~100% during playback and transcoding audio from DTS-HD MA to stereo.
So, yes you can use the DS220j but you'll likely get frustrated sooner rather than later and getting a better CPU and more RAM would be a worthwhile investment if media streaming is your goal.