Comment by eightys3v3n

Likely not the best approach:

I had ~200GiB. I selected below 10k files at a time to upload in the web UI (selected all 2014, then 2015). It was fine. More than that many and the UI became unusable.

External Libraries seem like a good option.

They have also recently improved the background import in the Android app so I have heard so that might be worth a try.