Congrats on your decision! What school do you plan on going to?
As far as advice, you should just know that there is no one job at Universal where you just get to draw up ideas for lands and rides--it's all balancing a lot of projects. Some projects will be your brainchild, some will be others' that you have to help with the grunt work on. There are big exciting projects and then there are projects that involve changing out artwork in an element you've probably never noticed before. Sometimes working on the details of a project that you're not leading can be daunting. But for the most part it's a lot of fun and cool having a hand in what millions of people see and experience.
One thing you should know...UC itself is a small department. The vast majority of guys working on Kong, for example, are contractors and freelance artists. Once Kong is done, they are jobless. It's not so bad now considering Universal has so many projects going on right now that these guys can jump to but the climate is always uncertain. Think about the famous story of Beastly Kingdom...those guys that got laid off and picked up by Universal to design Dueling Dragons were, for the most part, contractors. That's why that story works as well as it does.
It's a great thing to study if you have a passion for it but the idea of Creative/Imagineering gets kinda romanticized I think. It's still VERY cool, but you should know how it works. Another important thing--focus on you and your skills. Build a good art portfolio and make relationships...that's really how to get jobs in this industry. Good luck and be sure to chime in with info about all the rides you'll go on to design!