I see this becoming more and more common. I’m not entirely sure if it is a trend with legs, but the best practices are the same with managing any community.
Reward people for being part of it.
Do 5% or less of the talking and promoting (it’s all about them, not you.)
Make sure on your part, and encourage on other’s parts, to be clear and direct whenever possible to ensure everyone understands what’s being said.
This is a personal one: I have a hard time reading Slack messages because there’s no tone of voice. So sometimes things that could read as aggressive are not meant to be at all. To counter that, I use a lot of smiler faces and winks to indicate mood. Don’t hesitate to do the same.
Make sure there’s an offline function. You don’t want 100% of the community’s interaction to be through Slack. Do meet-ups. Do events or small get togethers with members as you (or they) come to town.
Foster a safe and positive environment. If in the event that you DO have an asshole as part of the community, give them three strikes, but on the third, hold the line and kick them out. If people feel like they’re going to be attacked or not heard, they’re not going to post. You can have big, strong discussions, but don’t allow any sort of personal attacks or trolling to escape unnoticed.