It'd be hard to overseek, for I noticed the amount of scammers and just freaks who always want to post something ridiculous in public servers. Also it allows us to share and discuss previews of Patreon content.
I have some suggestions: you could make the patreon talk in a donator only channel (make a role that is given to people who support) that will be privated to only that role or you could make a no payment member role that restricts access to channels that show patreon photos, leaks, and information. about scammers: You could get moderators or helpers to filter through content here and there to make sure the rules stay in tact (I could moderate for 100% free if you really wanted)
To add on: if people join it, they can ask for help and get answers from people more frequently than from here.
With your reasoning, I understand how opening the Discord could allow things like that to occur. I do agree with Mystery's suggestions and how using moderators would cut back on Scammers or Bots from joining and roaming around the server. The benefits still possibly outweigh the negatives though. Having a more central location where people could join and see progress may result in more people discovering your work and possibly adding more popularity and funding into your project and or future projects