Real time chat environments are not conducive to long form communication. I've never been a part of an organization that does long form communication well on slack. You can call it a boundary issue - it doesn't really matter how you categorize the problem, it's definitely a change from email.

Regarding #4, I can't turn off my online/offline indicator, I can only go online or offline. I can't even set the time it takes to go idle. These are intentionally not configurable in slack. I have no desire to have a real time status indicator in the tool I use to communicate with coworkers.