I think you have just put into words what every parent of a wish child is thinking! Or even people like me just helping plan!
I totally understand your feeling here - this is THE trip - the one you have been planning for months - and you know you can only do it once. So I totally get the panic...
I wish there was some way I could convince you that it will be an awesome trip, but it won't be perfect - and you will still love it!
To give you an idea - Lauren got really sick on her trip, spent the night in the hospital and missed basically two park days - and STILL says it was the best trip of her entire life! We had plans to visit every wish lounge, MK, Epcot, DHS, Sea World - and we only made it to MK and DHS and spent just a little bit of time at Sea World. And it was still completely magical! They were even sweet to her in the hospital. The magic followed her everywhere.
Remember that you CAN spend some time at GKTW when you ever return to the Orlando area. So if you miss something there, you can always go back.
The one thing I read over and over in trip reports is that they all had a magical moment - a time with their family that they cherish - but for each family it is different. For some it was just playing together at a playground - something that was not planned at all, just happened. And for some it was a party that they really enjoyed at GKTW. For some it was a special character encounter. But for most it was something that was
unplanned and something that happened with the family just went with the flow of the trip and allowed their plans to bend.
All of your planning is really going to help you - because you won't be spending time on your special trip trying to even decide what you want to accomplish and miss lots of things. You will know your way around because you have put so much research into it. You will know what other things families were able to do and have an idea what may be accomplished if you get a great CM that will help create some magic - and all of that information will make your trip more magical. The fact that you planned ahead will help you so much!
But once you are there...try to let go and just let some things just happen. Sometimes the best thing you can do for your family is to take a rest day, watch a movie in the villa and order pizza - something that seems totally crazy as you are planning - but will be a memory you will cherish forever.
It made me laugh - last year Lauren was interviewed by a radio station about her trip. She told them she got sick and that it was the best trip EVER!
When they asked her what her favorite part was...she said it was "standing in the rain at the castle watching the light parade!"
I would have thought she would be disappointed by the rain - but it was her best moment, it was fun playing in the rain.
Have fun. Relax - as hard as that sounds - and you will really enjoy yourself. Take it all in. Enjoy every minute of the trip, even the parts you think you will regret later - it is all just part of it.
And after all of that blabbing...I don't think I even answered your question! Sorry...
Here are some answers: You will get the info on Wish Lounges when you do your GKTW orientation. They will explain where they are and give you a special VIP code to get in.
Must Sees and Must Dos - really are all up to you guys. For us they were seeing the light parade and Lauren feeding the dolphins. But they are different for every family - ask each member of your family what one thing they would be disappointed to miss and those are your must dos.
It is possible to ride on a parade float - but very few families get to do it and it is totally random. They don't pick wish families for those things, usually.
Getting on stage: There are several things where your child is more likely to get picked to be onstage. Here are a few:
Jedi Training Academy - get there early and make sure they know you have a wish child, you should get a ticket of sorts to be able to participate.
Lion King Show - Get there early and they should sit you in one of the front few rows (make sure they know you are on a wish trip), and being up front will increase the chance that your child would be picked to participate in something.
Beauty and the Beast Show - Usually ONE young girl is chosen to pick up a rose from the Beast at the end of the show - if you have a female wish child and get there early, you could ask if they could do this or they may just offer. But it is possible they would already have chosen a child.
MK Fireworks - this may be less random. Ask...It never hurts to ask! There are CM's that have ear buds in their ears and are usually carrying little trash picker-uppers...(gosh, that makes no sense)...little hand grabber things to pick up trash. Those are, often, managers - and when I have a problem or something I need them to do for me, I try to scout out one of them. They may or may not be able to help you, but they are more likely to have the power than a typical CM. This is true for anything during your trip that you may need.
Wear your wish buttons - all the time - and have every member of your party wear them. Wear every sticker and button they give you - this will help make sure you are spotted, even in a crowd.
Always, always have your camera with you and make sure it is fully charged (with extra batteries, if you can) - because you never know when the magic will happen and sometimes it happens at the oddest of moments.
Have fun! You have done your homework and really planned - so once it comes, just enjoy it. Let people wait on you. Let this be your time with your family to do what you would all like to do.
Have a blast!!
Hope it's a great one 
