Hi!:wave: We've gone to Disney when both of our kids were 9 months old. You can pretty much take her on anything that doesn't have height restrictions (Dumbo, Small World, Peter Pan, Pooh, Aladdin, even Pirates and Haunted Mansion). In Epcot the rides are longer so you have to judge whether she'll sit that long, or if she'll likely take a nap (SpaceShip Earth is a long ride, great for napping). Shows can be done too depending on and if she'll sit. Each child is different, we had a lot of luck with both of our kids.
We've never done a water park with the kids. If it's just the three of you I wonder if it's worth the extra money.
Try AAA for rest stop info and how long it'll take. Yahoo Maps or Mapquest should also be able to give you a good idea.
Most importantly your baby needs to be in her car seat the entire time that you are driving. So, all changing, burping, feeding (unless it can be done in her seat) you will need to pull over. It is incredibly dangerous (and illegal) for you to travel with your child not in the car seat.
Other tips: bring some favorite toys and a strap that can attach to your stroller so that they don't get lost. Bring Cheerios (if she's eating them) with you or other small foods that can be good distractors and also to make sure that she's eating enough and when she needs to. Both of our kids didn't eat as much when we were away so we tried to have the things they really liked so they were more likely to eat. Make sure she drinks plenty. Ask your doctor about how much water and how often she should drink (you can drink too much water, and it's easy for a baby to drink too much). Make sure you buy baby sun block. She'll just be old enough to use it, you want to make sure you get stuff that is safe and remember you can get a sunburn even if it's overcast.
Character meals are awesome with babies. If your little one is able to sit up in a high chair and isn't afraid of the characters the interaction can be awesome. The characters are incredible with infants.
I hope this helps! Have a great time, both of our kids loved being in Disney at this age.
Also, the fountains downtown were a huge hit!