I think 320 might be a bit high.
I'm just over half-way there.
maybe 220 might be more achievable.
You can always move the goal posts. when someone hits top spot they can revel in the glory for a month and then you adjust the number so they need another hundred posts. That could also be a good time to change the monster type.
I think next scale will top at 250 then 300 as we beat each one.
The dates for events posts would be great,
if anyone wants to add a post for that so everyone can add to it,
just start a new post under "world bridge" section as it visible even if not logged in,
then all of us can add to it if we find more / new events worth posting.