When the wish granters come they will spend time with both you and your child and determine what wish is the correct one for your child. In other words just because you want to go to Disney does not mean that you will ge tthe trip. (NOT being harsh this is EXACTLY the way they put it to me.)
You child must have a couple of things theat they wish for (For us it was Disney and then a playset) They will walk you through a LOT of paper work (releases and doctor forms) They may ask for tentative dates also. If your child's wish is for a character dining they MAY provide it. I booked one just in case, because they are keeping everything secret to surprise us!
From there you have to wait for the medical forms to be sent by your doctor stating that DD/DS can medically go on the trip....They may/may not have the answers that you are seeking because these are NOT the ones who determine if you are going...They just prepare the paperwork and submit it into the chapter.
Feel free to ask questions. Let them know what medical equiptment that you need ...for example IV poles, nebulizer O2 concentrator and the like...as far as a rental car my MAW asked me what I would like ie minivan or lift van. I told them I would need a booster for my son..We are taking Eva's car seat on the plane so I did not need a rental. Some MAW provide diapers mine is NOT. I am also needing to ship my formula down to GKTW ahead of time (cheaper than checking it on the plane.)
Let them know if you need a stroller rental so they can look into it.
I hope I have helped a bit with your questions.