Again I suggest the idea of those who are going to have a conversation or group activity shall post together in a group PM with each other a number of posts per group then post the bundles of 4-8 to avoid TL;DR and speedposting walls.

If 2 people are posting, then they can each post up to 4 times each at max before sending the bundle out 3 people could each post twice and send out six, four people could each say two things and send out a bigger set of eight, anything more than that i think would be too much to do in a posting set without including others.