Don't make it sound too complicated. Guild sparring isn't single spar. You just need five members that are capable of adapting zoning technique. Zoning is the most important skill in the guild spar. I don't recommend any teams to use the wall strategy, because if you wall you won't be having a space to dodge and become very predictable. It's best to have members that can charge in and pressure the enemy as a team, eventually the enemy will run out of space to dodge and will try to escape from it. However this technique doesn't work on foreign players, which is why I had such a hard time getting at them.
It's also important to remember not to die or lose your health fast. I've watched some of my past GST footage. My teams lost because of me dying too early. It was pretty much 4v5 for them, even though I roughly gave in about 5-6 hits.
Last but not least, the person in the center should be able to handle any opponents in three direction. Assuming that your back is covered, the person in the center can act as a support and pressure the enemy one by one and eliminate them as a team.
Every team has their own strategy. I personally do not discuss anything with my members, but I just happen to choose the right person to use. Practicing naturally helps a lot, but don't over do it or your enemy will read every one of your moves.