I have a DS220j. Being new to the world of Nas, I didnt realise that its not very powerful so ended up getting a Raspberry Pi 4 to go with it, which actually ended up costing less than a DS220+ which is what I should have got.
1 * 12tb Drive seems to be more than enough at the moment. Photography is a big hobby for me, so the Nas is perfect for backing up all photos from Laptop and phones, as well as a full backup of the laptop. I also recently ripped all my CDs to MP3s so they all live on the NAS also.