1. Yes, absolutely. The overwhelming majority of students who score in the 2300-2400 range have studied significantly – whether that be independently with books (which is completely viable), or with a larger course and/or private tutor.
2. In my entire life, I have met one person who actually got a 2400 and did not study. Many people claim to have gotten a 2400 when they didn’t. Even more people who got a 2400 (latest statistic i’ve seen on this puts the number of perfect-scorers at ~400-500/year) claim to have not studied. Usually, they aren’t being entirely honest.
Short answer: Study. Study hard. If you have to ask this question, chances are that you are NOT one of those people who can ace the test without any preparation. Better to assume that you are a part of the unlucky majority that needs to study hard to get decent scores (I, myself, am a member of this group), than risk it.