I think the most important part of gameplanning is doing the opposition research. The U21 manager needs to do more than just lead the discussion. They have to do their homework and make that they have all of the information ready before you can even talk about tactics.
I have a chart with the complete history of each opponent's games including Score, Result, GDP usage, whether the GDP was correct or incorrect, did they use enthusiasm, and all their game ratings (OS, IS, OD, ID, RB , Flow).
In addition, I do extensive opponent personal scouting. I post all GS/DMIs in order to predict what players are going to play and what will play . It's also important to know what players a team likes to use in each tactic. If you know that your opponent uses a certain player to play LI SF and another to Neutral SF etc., analyzing the DMI/GS of your opponent is a good predictor about what tactics a team will play Since GS has sub levels (low, mid, high), its important to track your opponents DMIs from week to week so you have a better idea how certain players are going to perform.
I also keep a database of the skills of all opponents that are put on the Transfer List. Even the starting skills of a 18 year old player that is put on the TL after the draft is useful in finding a weakness to exploit (like a big with 1 or 2 OD).
After that on Friday after the training update, I post a chart of our players with skills and GS to help you pick the best tactic for that week. Only then can the discussion really start.
The offsite was created to ensure a safe and secure place to discuss tactics without other nations seeing. All people who register for the offsite not only need to be a USA manager but are checked through our forum security to make sure their IP address is from the United States and they are not using a proxy or VPN.
Any USA owner can register for an account and contribute to the discussion. The idea that there is some small group of owners controlling the offsite is kinda of funny coming from someone who wants to create some secret email chain and have a small cabinet of "trusted owners". Doesn't sound like a community to me. During the finals, IIRC nearly 20 patriotic American BBers contributed to the gameplanning. The more people that contribute the better IMHO. Different perspective give you different insights that you can use.
But in the end advice is advice, and the manager is the one that has to make the tough call.