First, nice article. It appears well written, is in a good "order of revelation", and includes the code in an easy to read format. Kudos for all that and thank you for sharing.
I do have to ask, though...
Why not just put a nice, set-based trigger on each"ETL" table that captures the row count and date along with the trigger action and write it to either a separate log table for each "ETL" table or to a common table for all tables? If you elect to use one log table to each "ETL" table, the trigger could easily be built to create that table with almost no overhead so that someone wouldn't have to remember to do it. The reporting would be super simple, as well. You could even capture what did the action using something like the ORIGINAL_LOGIN() function.
Most of the code being executed in Python for this is T-SQL anyway and has code that is proprietary to T-SQL so it's not going to be an instant "drop it in and run it" solution, anyway.