There are already Discords based around Cave Story. In fact, there's a Discord server for these forums that's been around since 2016. You can find it here: https://discord.gg/0l4989hIisKn4fJ6
There's also another one that can be found on the Cave Story Subreddit. You can find that one here: https://discord.gg/bE7PSnV
For the main Cave Story discords (barring the reddit one), the CSTSF server was made official by Dunc, the CSMS was made official by BLink and Enlight.