I do understand the choice of slack over irc (you can just login from every browser and not lose chat history) - but it seems weird to me to not have a irc channel on freenode which is, i think, still standard.

There are discord bots who link discord and irc, I guess the same would exist for slack.
The question about moderating another channel would not apply, since they both will be the same channel.

Either way good news on the invites of slack opening up