I just created a new digitalocean droplet (the 16GB droplet) to try and see what the database size should be, and I'm just following the script you show in this post. Hopefully the database size will end up being the same as yours (currently around 419G) or mine (currently around 370G) and not be some new number. Right now the mysql database size per the size of _data/steem on the new droplet is at 5G, and I plan to periodically check on the progress of the database size over the next few days.

One thing I noticed is that "mysql -h 172.17.0.2 -u root -p" gives the error "-bash: mysql: command not found" and I wanted to bring that to your attention because I think it means you'll want to adjust the script you show in your post.

One other comment I wanted to make regarding tests with droplets and volumes is that the storage volumes that are created when creating a droplet aren't actually deleted when the droplet is destroyed and there is a separate step to destroy a volume. I actually had three $50/month volumes that I wasn't using but still being charged for which I incorrectly assumed were deleted when I deleted the corresponding droplet. Fortunately, however, I noticed them and deleted them after only a few days.