Discord will definitely foster a more engaged community where people get to know each other better, but keep in mind you would really need to hire a moderator to keep things on the rails - to babysit it. Just given the real-time nature, this is likely to be the case if there's more than a couple dozen individuals.
Your participation level matters a lot as to making the decision: if you plan to be available for people to chat with you often enough, the Discord would be way, way, way more popular than this forum.-[=pp0-po=\oi On the other hand if it's once in a rare moon, the forum format will be better because a post from a weeks ago either is going to be easily reachable and or at least possible to be pinned if the forum were too busy.
On something like Discord or Slack things are kind of ephemeral. Which has its own advantages.
I do like forums, where I can get bakc to threats and it is not consumed in the latest whatever thingys.
As I have no idea what Discourse is and what the platform can do, I stick with the old, like the aviation industry does (Who needs USB drives, when you can have floppy disks?)
Little late to the party, but I do use discourse in another forum. It has quote and reply features but mostly it can handle a lot of traffic. I forget if we were on PHP or vbulletin or yet another one at the time but the sheer amount of posting was killing it. Forum was Chronicle of the Horse if you want to look at the differences. https://forum.chronofhorse.com/