Thank you for taking the time to discuss this with us, and to explain in more detail how you envision this to work. You have already answered and address most of the questions / concerns that I had. There are still a few things that I would like to have clarified.
1. How will this work with F2P and packs that they may not own? Will they even be able to see it? What happens if they try to join something that they do not have access to?
2. Quest Chains. Will you be able to post for an entire chain, or just the quest you are currently on? What happens if someone wants to join you, that is not on the same part of the chain that you are on?