4 is worthless. 3 is OK for beginners, but you pretty much need 1 to get a job here. That said, the JLPT is not much use unless you are trying to show that you know Japanese, either for a job or graduate school, unless you just want to study to see how it goes (the JLPT prep material makes good study guides).
iffy, it depends on what you know. I've known people who have studied for years and don't know more than 20 kanji.
I've used a few different textbooks, but for beginners I whole heartedly recommend Genki 1 & 2, published by the Japan Times, which I used at my university, Emory, and Kansai Gaidai the year I spent there. Going through those, with a native speaker, you can probably take 3 easily by the end of book 1, or the middle of book 2 at the latest. It has a really good section on kanji as well. By the end of the two books, you learn a lot of the most commonly used kanji.
For intermediate I used Kansai Gaidai's Level 4 conversation book and I don't know a good equivalent for it. For advanced, the Japan Times' From Intermediate to Advanced Japanese is a really awesome textbook, but you need a teacher to get much use out of it.