Thank you so much for taking the time to give you quick tips...those help out tremendously!!! I guess my husband and I really need to take a night and sit down to start some serious planning! I know we will not be able to do everything in one trip, but I do want to make sure we get the most out of our trip.
I have a few questions:
1- I have 3 girls. My wish girl will be 17 at the time of the visit but she has Rett Syndrome. So riding rides will be out for her for the most part unless they are "calm" rides. What do you guys recommend in MK for her? I went when I was 12 and I do not remember much at all...so any advice on something awesome for her would be great. She is, what the schools will tell you, mentally of a 6 mth old or so. She LOVES lights but not strobe lights (has epilepsy) and LOVES characters. She loves animals and absolutely LOVES Barney & friends.
I would highly recommend the book Passporters Open Mouse...mainly because they will tell you which rides have the strobe lights. I know Buzz Lightyear has a strobe light, but I can't remember what other rides have one. Some of the shows will have some, too.
I think you will be happy about how many things she can ride! Lots of slower and calmer rides - more than a typical amusement park.
The book I mentioned above has very detailed information on every ride, but it is a little dated. I would still get it...it will help you a lot...especially with the strobe light issue!
Honestly, she would probably be happy just going around the parks and meeting characters and watching the shows. The rides she can go on will be a bonus.
My 8 year old can ride rides of any kind-she is tall and is a dare devil. Will they allow her to the front of lines if my Wish daughter is NOT riding that ride? What do you recommend for her as a "Must DO".
This is sort of a gray area...someone may disagree with me here...but yes - they will let her use it. She just needs to either take the button or the GAC and tell the CM that the GAC/button belongs to her sister, but that her sister is waiting for her - the CM's really want wish families to get through the "system" quickly so that they can get on with their trip - so they treat the whole family like VIP's.
As far as rides...Roller Coasters - the biggest/fastest is Rock n Roller Coaster (RnR) in Hollywood Studios. Tower of Terror is there, also - both fun and daring.
Animal Kingdom has Expedition Everest, which is a roller coaster that goes backwards in the dark. 
MK has the big three - Space Mountain, Splash Mountain (water ride with drop at the end) and Big Thunder Mountain Railroad (a calmer coaster, but still fun).
Epcot doesn't really have any major ones...Mission Space has a side that spins more and that is fun! Test Track...I guess that could be considered more fast paced.
Soarin' is a do not miss for anyone that can ride it!!!
My 4 year old is a Toy Story freak and loves Princesses too. Anything Disney and all of my girls are finatics. I am curious as to what is a Must so we can plan accordingly.
Make sure you ride Toy Story (at Hollywood Studios) early in the day so that you can ride it again and again, even if your arms hurt. You may want to take a break from it and come back to it later. For me...3 or 4 times in one day is about all I can handle before my arm starts hurting from the shooting game and my 2nd ride is usually my best score.
That is a great ride! I used my Give a Day/Get a Day fastpasses on it and rode it a bunch of times on my last trip. 
Make sure they go to the Princesses and Fairies meet place - it is back in Toon Town right now...but check when you get to the MK.
2- Do you recommend any Character Dining that gives you the most Characters visiting? Which Character Dining do you like best and why? We would like to have one dining experience for the girls to remember.
Honestly...the character dining is pretty fast moving at most of the restaurants...especially during a busy time. I would pick the restaurant based on the characters they want to see...but keep in mind that your button/GAC works on character lines and you can really see all of them i the parks without really waiting very long at all. And they usually spend a good amount of time with wish families. 
I have heard of a few stories a while back where 1900 Parke Fare was doing some special meet and greets after the Dinner time for a couple of wish kids...but that is completely random and you can't count on it at all.
Just have them look at the opportunities and vote. I would skip the castle unless they are just really wanting to eat there...the food is crummy (in my opinion
).
3- Which other parks are awesome for my girls? I don't even know what parks are all there... I guess I need to research that as well! YIKES I am so overwhelmed!!!
Keep in mind you can't do it all...really...just have each member of your family pick the two things they want to do in each park. On our trip we intentionally left out Universal because Lauren could not ride much there...but we regretted that later when I found out how awesome they are for wish families (front of the line VIP access). We also never even got to Epcot or AK on our trip - so we are planning a trip back.
I would pick three parks they really want to see and pick 2 things per family member that are their must do's - do those first and then fill in the rest of the day with more things on their list.
4- What is the Big Give I keep hearing about? I am curious as to what that is and how it works?
Let me answer this in a bit...I have a patient...I will come back to this...
Edited to add:... Looks like someone copied the post I wrote a while ago about it...that is basically the gist of it.
Thank you for your time again....