I've planned many, many trips for our big family group. Last year, we had 12, but there are many that were larger. I've learned some lessons along the way. My first suggestion is to drop the idea that you'll be "traversing the parks in such a large group." If you all decide to stay together, that's a great plus! But insisting on it will only bring you heartache...
Before we go:
1. I also love the planning! So I make a great plan. Dining reservations, Fastpasses and which attractions to visit in what order are all planned out ahead of time. For newbies traveling with us, the more detail the better.
2. I build anticipation with a Facebook event page. I poll the group, send information about attractions and dining, and usually include a schedule for watching Disney movies (Disney movie of the week!)
3. I create a GroupMe chat. Great, great way to contact the whole group at once and invaluable once we get to the parks.
3. I usually create a booklet with everything from our flights (or driving routes) to daily schedules to a list of reservations and give one to each person. They have become great keepsakes. If you're not inclined to do that, then just make sure the schedule is easily accessible digitally. Make sure everyone knows how to access it.
4. I used to make us family t-shirts and that is still fun, but last time I ordered personalized cinchbags for everyone. To my surprise, they all used them to carry their stuff while in the parks. The date and "name" of our vacation was on each bag and I kept the cost down by putting names on them myself. I also put in a few items for each person to use in the parks, including a portable phone charger. The blue bags and white lettering helped us identify each other from afar while in the parks!
Once there:
1. Because our group is now older, I let everyone do their own thing. I make the plan, publish it to the group, but I don't force it. If someone wants to sleep in, I can explain what they'll miss, but I let them guide their own vacation. It's their choice whether or not to stay with "the group" - but usually they do.
2. I don't make myself responsible for everyone's happiness. I try to give them as much information as possible to make their own decisions. But if they are late for something and miss out - not my problem.
3. I plan one meal a day that I ask everyone to attend - since they aren't "required" to do anything else, this is usually something they like.
4. I use GroupMe to communicate with everyone in the group at once while we're in the parks.
5. Each evening. I send a GroupMe with the events for the next day. The park we're visiting, what time to meet up in the morning, where we'll be eating, etc. Again, I'm only responsible for making the information available. I let each person decide what they'll do with it.
6. If people do NOT plan to follow the plan for the day, I ask them to let me know so the rest of us aren't trying to wait on someone who's not going to show up...
7. If you plan to share the cost of meals (or anything else), get and get familiar with an expense-splitting app like Splitwise and Plates. They aren't perfect, but they help. Keep up with it each day and insist on quick reimbursement. Don't let it slide or it can be the source of some bad feelings.
Observations:
1. It usually only takes one day of missing out on a great ride that needed to be done early (to miss the long lines) for the members of our group to "get" why I did such extensive planning - and they're usually be right there with us the next time.
2. Having one meal together a day means we are able to see each other's faces and enjoy each other's company at least once a day, and it's usually a welcome respite.
3. Our trips with people who have never been to the parks before usually start with everyone pretty much following the schedule the first day at each park. If we visit a park a second time, they tend pick and choose which parts of the plan they want to follow.
4. Once, I did not plan out a 2nd day at the parks, even though we were visiting them twice. After seeing how it works, and understanding the plan was a good idea, my group was disappointed to not have a "2nd day" plan. So now I do one in case someone wants to use it.
5. Not making myself responsible for the happiness of others, or their choice of schedule, has made my life MUCH easier and our vacations much more enjoyable for me.
Hope this helps a little. Have a great, great time!