Reddit mentions of Colloquial Japanese (Colloquial Series)

Don't worry about the N# levels, they really don't indicate your skill at all. Many people have studied for those tests specifically and had no skill in Japanese other than those tests, and still managed to pass N5. It doesn't test you for anything other than reading.

For learning hiragana and katakana, you can do that over the weekend and the kanji you can learn in two or three months. Personally I'm doing 50 a day. You should look in to a tool called Anki, and some books. Specifically, Teach Yourself Complete Japanese, Colloquial Japanese and GENKI I: An Integrated Course in Elementary Japanese. Send me a PM and I'll see what I can do for sending you some E-book versions of those books.

For Kanji, check out Heisig's Remembering the Kanji. There's a shared deck for it on Anki. I changed the particular deck available on Anki so the kanji is on the front, and the meaning and the story are on the back. It doesn't teach you the meanings of the kanji, which I believe is a good thing; you should learn the readings of the kanji from the context in certain words. I'm currently learning 50 new kanji a day with Anki + doing my reviews.