I've tried to write something similar, but I found that I was hitting the upper comment limitation of reddits API (ie. If there are more than 10k comments on a subreddit within an hour). How did you get around this problem?
You can see exactly what is monitored here: https://f5bot.com/what I'm focusing on mostly programmer related subreddits for now, but I'll add subreddits as people ask. I had a couple people ask yesterday for me to add specific subreddits, and I did.