Some people mentioned that official discord will take a lot of time from game development, but from my own experience Discord will not consume development time - it is possible to chose some volunteers as moderators and allow them to do most moderation work. Discord is a good place for community to discuss things, and sometimes (but not always) it works better then forums. That's why some projects have both Discord and Forum (Minetest, for example, or some large mod projects)
I think only one person has to start with it
The problem with such approach is that the owner of server has a full control over it, and if he is not one of game developers - there can be consequences. For example he can abandon server, and if server don't have moderators - it will sink in spam, fishing links and other bad things. Or he can become mad at one moment and do something really bad with server or its members. The best solution is when the owner of the server is, well, same person as the owner of the game, and moderators are his trusted people who take care of server while dev is working on the game. In that case both problems will be solved together as in case of any conflict the server owner can easily solve it, and even if one of moderators will lost his control - effectively solve it