I've done a number of group trips to WDW. If you are planning a wedding, that's more than enough to plan. If you can find someone else to plan the WDW part, that would be prudent.
It isn't just the planning, it is being in charge when something doesn't go according to plan. Let someone else own that.
I personally stopped planning for groups when the no-show fee was added to ADR's. If you make Dining reservations- ADR's- and someone doesn't show, YOU will be charged. Even without a wedding, I do not want to be responsible for that. that's like loaning money to relatives- VERY bad idea!
To make a group work- where you stay together- everyone has to wake up and go to sleep at the some time, more or less. You also need to coordinate all food/snacks. You ALSO need to coordinate BATHROOM breaks. (Our rule, "when one goes, we all go!") If you don't, then you can need up spending most of the day standing by the bathroom with an melting ice cream dripping down your wrist.
In my experience, adults don't like another adult telling them when they can eat/use the restroom.
So....if you want to be in charge of a tiny subgroup, go for it. Otherwise, maybe share your plans, with everyone, (maybe) but let them own the rest. Set the bar low: invite your big group to meet up for one attraction each day. Preferably something like Small world- where your group can sit together and EVERYONE in your group can ride (kids? grandma? someone who is pregnant? someone who hates coasters/spinning?)
Tell the bigger group where you plan to eat, but let them be in charge of their own $ no show fees. OR meet up at a quick serve place at an off time: 11:30am, or 2pm. (Not BOG!) Pick a place with lots of seats like Starlight Ray's, then deputize someone to coordinate the meet up.
Also, very big groups at ADR's is a just a pain. Many times, our large group was seated WELL PAST our ADR. Any place that isn't a buffet or ALCE will be a slow meal. As volume oriented as WDW is, asking a chef to make 16 dinners at once is a challenge.
Now if you HAPPEN to be staying in one of the LARGE suites at the deluxe hotels, then you COULD have a meal or snacks/appetizers delivered to your room, or send someone out to buy drinks and snacks(groceries). You could also easily meet up together in a lounge if you are all staying club level, or a place like a Hampton Inn - which already has a breakfast lounge. At a open lounge, people can come and go and get food as the please- much less stressful than having all eat together. A food court could also work, as long sa you avoid the breakfast RUSH hour (8:30am to about 9:30am)
With 16, that's going to be kind of key. It is more or less impossible to find 16 people who want to spend a full week together. Much better if they can come and go when they want, with no pressure.
I don't see where you need to tell them how to use
MDE. Most folks can figure it out. Like I said, share your itinerary, but let them own their own choices. Adults like that.
Than again...if everyone has transportation...it may be possible to have a coordinated offsite meal. There are many offsite options around Orlando, where you could all meet up for happy hour or something that wouldn't require an ADR. There's only a few onsite that would work for that kind of meet up, but most WDW gets pretty packed at anything resembling normal dining hours.
If you do end up doing it be sure to get everyone linked and then they have to give you permission to see their photos, if you are doing Memory Maker. Been awhile, but I think you have to get them all to approve your request to alter their plans too, which would mean to make their FP+s or maybe that is just part of the linking. Be sure to get it all done a few days ahead of booking day or you will go nuts trying to get them all to approve.
