Update:
So I have been running calibre without "--ignore-plugins" and performing my normal tasks. Here is the result of the memory usage:
Start of Application - 1,128,176k RAM
Date: 8/22
https://i.imgur.com/iAR7ETI.png
Next Day - 5,772,288k RAM
Date: 8/23
https://i.imgur.com/iD2ZbCP.png
I didn't touch Calibre for a few days, but all of the automated calibredb processes were still running. So, no metadata downloading or editing, and it came out to this: 5,659,696k RAM
Date: 8/26
https://i.imgur.com/pWXlBhJ.png
So it seems as if the "leak" occurs only when downloading/editing metadata, and also seems consistent when running with "--ignore-plugins"