1) Depends why there's a gap. If you were in school or something, it'll be obvious.
2) Emphasize in your cover letter what does transfer over and why you want this different position - not "I'm desperate enough to apply for anything" of course.
3) Education, college should always be on there. Plus relevant certifications, etc. No high school. Experience, as far back as you want as long as jobs are relevant. If you have a ton of experience, you can leave off that babysitting gig.
4) It's not. Everything I've read lately from professionals suggests that's mostly a legend. It should be under two, however. Let your experience dictate it; if you have to scrunch everything down to three-point font to fit it on one page, don't. But if you just barely go over one page, see if you can pare it down to one.
I agree with everyone else that if you're in college you shouldn't go over one page. But it sounds like your presentation is more general - you didn't indicate if it was aimed solely at college students.
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