I'd say a valid approach is try one of those numbers for couple days and see what happens. Another approach is splitting users into 2 groups and one pays X and the other one pays Y and then measuring the effect (i.e. if raising the prices actually reduces spam and how much SN earns from spam). Here you can apply all new proper H0 & experiment design skills.
Just trying to brainstorm through the context from the other side of the problem (and I'm going to be making stupid math assumptions, so don't read too much into it):
How much time do users spend consuming posts and how many sats on average they spend?
  • The user side of the pairing is that they have let's say ~1hr per day to consume the best posts that match their needs and interests.
  • The users are willing to pay at least [average sats] for this.
  • Let's say that users want at least 80% of good content vs bad to make it worth it.
  • Users can spend 20% of their time on curating the bad content without getting annoyed and leaving the site forever. So this would mean 10 minutes per day can be spent on curation.
  • With 2k users this would give 333 hrs of "free" curation work per day (but likely way less)
  • 333/[average time to recognize spam]/[people needed for spam consensus] = number of spam posts the SN can handle per day