The JLPT doesn't prepare you or test for communication skill at all, so no JLPT level will make you fluent. It's possible to pass N1 without ever speaking to another person in Japanese, or it's possible to be conversational with very little grammar and vocab knowledge, so the test is just not a good measure to use if your goal is fluency.
Fluency is about your confidence level USING the language, and it means something different to every learner, so what amount of grammar and vocabulary knowledge you need to be fluent is completely dependent on your own personality and language goals.
Hi, I have been studying the JLPT vocabulary and kanji lists here for a while, although I have no intention of taking the test for now. I just wanted to reach some "proficiency" in understanding the language. After finishing studying the JLPT lists up to level N3, I can say that my knowledge of the written language increased a lot, I can now read most texts and have an idea of what they say. But as Gillianfaith pointed out, spoken language is another thing, I can't understand dialogues (especially when they speak fast) except for a few sporadic words. I agree that this level of fluency comes from daily use of the language and communicating with others.
I think that the way that the contents (grammar, kanji, vocab) are organized makes for a good guide on the order of how to study. There are a lot of things to learn since Japanese is very different from western languages, and having the jlpt order and study materials as a guide can make you less lost. You just need to supplement that with more listening and speaking.
It's better to watch japanese stuff to get more used to the language, as the listening questions and examples on study materials are quite boring. I would recommend tv shows instead of anime tho, since the language used there is way closer to how real people talk.
I think that only studying vocab from JLPT lists will leave you with a lot of holes in your knowledge for common use of Japanese, since there are also a lot of common phrases that don't get put on there. However, I have found the kanji section to be very helpful as a guide to read many kinds of documents and recognize meanings from kanji I know in new situations/compounds. As with any language, there needs to be a balance between structured "classroom" style learning and experiential "immersion" style learning for the greatest fluency gain. After all, even native speakers still take classes to improve their reading, vocabulary, and speaking skills at school.
