I'd be SO overwhelmed and excited! If it was a teaching day I'd have to contain it until I got home - I may not even notice it until I get home, I don't typically check Tapas or WEBTOON in the morning on teaching days - but if it was a comic drawing day, I'd set aside some time to read through and respond to all the new comments, as well as come over here and flip out a little bit in a forum thread. 
I'd also try to find out what was driving the growth; if it was a feature on Tapas or WEBTOON, or if a larger webcomic artist had recommended my series, or if the CANVAS team had retweeted one of my promo posts on Twitter. I'd want to thank the relevant people who did that for me. 
After that, I'd check back periodically across the day, to catch new comments and watch the numbers grow, (because it is kinda magical while it lasts), but most of my time would be just continuing to work on my comic. I can't let myself grow complacent because I had a growth spurt!
If I hit 1000, I'd also announce a Q&A. I want to do one, but I feel it's the kind of thing one does at either a major milestone for growth, or at the end of a chapter.