Honestly as long as they second message comes promptly after the first this doesn't bother me at all. It's when the "Hey" is just left out there by itself that annoys me.
It's very mildly annoying when it leads to me staring at slack waiting for you to finish typing, but if that's the most annoying thing that happens on slack that day then it's a really good day.
I suppose, as long as these 4 messages arrive in quick succession you're fine.
If you wait a minute between sending each, that's where you should feel guilty :P
The multiple notifications often bother me, but I think it's a problem with the messaging app, not with the sender. It shouldn't send a new notification for each message if it just sent one a few seconds ago.
I don't think the problem described is staccatto bursts (at least I hope, I do the same thing), but adding a synchronous element to the communication that doesn't add thing.
I think what you do is pretty in line with this ethos - the other person is pretty free to prioritize your messages as they see fit
Hey
Did you see that thread in #hn_feed?
I remember you asking about the right way to sand the wood before painting - some great ideas.
Also - cake on the 4th floor kitchen fyi
Since nobody in my entire office answers messages in the time it takes me to write those four, I struggle to feel guilty.