This won't be a full solution to these problems but may help a little.

It's easy for anyone to post spoilers and someone reads it before the managers take care of them, especially on the contest announcement.

So, how about we block wring new comments, at least on the contest announcement during the contest? I don't see a reason to enable any kind of comment regarding the contest before the contest ends. If someone has to say something to the contest managers, it'd better for them to be guided to writing through the question feature of the contest.