If you're doing it for the movies only, you will be better of with some NAS or the likes that let's you have an instance of JDownloader (Headless) and some Torrent client in order to download those movies while your macbook is asleep. It has also the advantage of being ampliable if it has let's say 3 bays and you use only one in the beginning. You also have some 8TB HDDisks which purpose is basically for Archiving, they use a new tech that crams more data in the same physical space, so they have a more limited read/write speed and life cycle, but if you only save the movies, and then maybe watch them once, or revisit occassionally, you should be fine with it.
Another cool option would be a Seedbox with Plex Server installed, you can even share with your family and have your own Netflix without that much hassle.
PS: I actually move the data out of the rMBP SSD after downloading, but prefer to download it in the SSD because it let's me juice up my 200mb symmetrical connection with no hassle, doing that with a regular HDD, not so easy.