in theory as you operate both the server and the bot you could modify lemmy to tell the bot when a new comment hits a thread instead of polling, which would be more efficient (but definitely harder to do!)
also does it handle the case where nobody from your instance is following a community? to make sure you get all the replies reliably the bot would need to subscribe to each community it's watching a post from
that said, great work. I may end up using it if I don't end up forgetting about its existence :p