I know that you can buy the cd ahead of time but I have a few questions. Is the $99. the final price or do you get charged for the pictures that you choose to keep and is there a limit to how many photos that you can have taken ?
It is the final price.
EVERY picture, on every photopass who's number you enter into your account, will show up on the CD, along with a copyright release. In additon, BEFORE you order your pics, you can go through an add borders, embelishments, etc to your pics...every time you do, it will add a "new" picture to your account.
For example, you have a pic of you and your family standing in front of the castle. You can take that pic and apply 3 different borders to it...you'll actually add 3 more pics to your account: The original, and one with each of the borders.
When we did this last January, we ended up with about 4 or 5 CD's worth of pictures. As far as I know, there is no limit to the number of pics, or the number of CD's. You won't have to "select" the pictures you want, because they send you EVERYTHING on the photpasses you link to your account.
For us, it's well worth it. My wife is the resident shutterbug, and she takes LOTS of great shots...but the one thing she can't take is full family photos...to hard to lug along a tripod and release cable.

And we get TONS of them, and then my wife spends HOURS doing the borders/embelishments before we order the CD.