How many active users are there?

No idea, my guess is 8k-20k

When did you start your list of 43k?

I've been working on the blacklist for over 2 years.

Does your list of 43k matter less if there
are not that many active users today?

43k accounts not 43k users. Many are farm networks with 200-500+ accounts. Many are not active anymore but I can't possibly track which ones are using any more and worry about them coming back to spam and plagiarize again.