Oh man!
You are going to have a GREAT day today! Because both of your questions/worries are going to be answered in a great way!
First of all...it is true that families staying at GKTW are given a Free PhotoPass CD by Disney. So no worries there! Just make sure you get LOTS of pictures with characters on your PhotoPass card (you are given one when you get to the parks) AND copy the number down and keep it in a safe place just in case you lose that card for some reason. It is a long list of numbers and letters. I take a picture of the back of the card with my digital camera AND phone AND write down the number...and put those in different places...to make sure I have the PhotoPass card info.
You can also end up with more than one PhotoPass card when you get to the parks for whatever reason (if you leave one in the room or your party splits up)...so you can technically have as many PhotoPass cards as you want and you just enter them in when you get back.
Then Disney will send you a FREE PhotoPass CD when you return.

Just PM me and I will send you a code.
As far as Tinkerbell...
You guys can TOTALLY meet Tink! You can meet her every single day you are at the Magic Kingdom, if you want!
Here are some thoughts on this:
1. You get front of the line access...the will take you through the exit so that you can meet her and the other faries that are there that day. You won't have to wait in line. And you can see her every single day you are there or more than once (but it may be different each time...

)
2. TELL every CM you see in the line that THIS is your child's wish - to meet Tinkerbell! Hopefully they will catch on and make it extra special.
3. The fireworks show at the end of the day features Tinkerbell....she flies across the entire park. You can tell where she flies because her "guide" wire

stretches from the top of the castle to the top of some building in Tomorrowland.
There are several GREAT places to see her fly...but you can sort of tell as you are walking around...where would be good. I like watching from Main Street near Casey's...but she is a bit far away. You can also look from the Tomorrowland bridge and get a different view.
You may want to be careful, though...because being TOO close could ruin the magic a bit...Tinkerbell can be a large pixie up close flying through the sky...and sometimes can have some masculine characteristics...just sayin. Tinkerbell that flies has to be very strong to fly all that way.
Here are some You Tube Videos of her flying...
http://www.youtube.com/watch?v=wu1Iuky8CqE
It happens after the beginning of Wishes...not RIGHT at the beginning.
http://www.youtube.com/watch?v=Mdrj_yqyPjI