Is taking a gap of a year for NEET 2017 a good idea?

It all depends on you whether you want to take a gap or not. If you are taking a gap make sure it is worth. If you want to clear your exam in 2nd attempt it is important that your basics should be cover. You can make your important notes which will also help you in revision. Before going to next topic you can prepare lot of problems. While you are on the new topic, practice high level questions on the previous topic simultaneously. Analyse all your mistakes from exam of last year and work upon them. After topic wise revision, you should start with test series, online or offline, quite early. As it creates exam-like environment, you come to know your mistakes and shortcomings and you can work upon them.