They don't ask you anything about grades or clubs. You just have to have good enough grades in your college career for your school to allow you to go. In most cases, thats just having above a 2.0 gpa I think.
The application doesnt ask you anything like that. Basically, its set up like your average application form you'd pick up at a store somewhere. They ask like your address, school information, previous work experience, and any criminal record you may have.
After that, you'll do a web interview. This is just a looooong questionaire set up like "I am always on time" and you answer strongly disagree, disagree, neutral, agree, strongly agree. Its designed to ask you really similar questions over and over again to make sure you aren't lying about your work/social habits. If you pass that (and you should) then you'll be given a phone number. You call that number and set up a time for an interviewer to call you for your interview later in the week. The phone interview is the only time you have an actual conversation with someone from Disney. They'll ask you two or three questions about each role you've selected as well as general questions like "why do you want to work for disney?" "how comfortable are you with people from other backgrounds?" "talk about a time you got through a stressful situation"... stuff like that. Then you wait, then you get accepted, then you move to Disney World!!
Pretty much, what you do in High School wont affect getting into the college program unless you just dont get into college.
Also like the previous poster said, check out the Disney Career Start Program as well and see which one you like better.