1. Hiragana/katakana can be learned in a week or two using flash cards and spaced repetition. It can be mastered through reading Japanese text for a few months to the point where you stop thinking about it. You don't need a $77 book to learn this, its just brute force memorization. I didn't know any other Japanese going in besides this.

2. Full immersion while ideal is impractical for most people interested in studying this language. You can still give yourself full immersion while learning anywhere in the world by using Japanese learning resources and limiting your English use to the minimum necessary (dictionary lookups, explanations for particularly troublesome concepts).

By the end of MNN 1 going into MNN 2 I swapped from a JP -> EN dictionary to a JP only dictionary. If I didn't understand a word from context in the book I would look it up in the dictionary, if I didn't know a word in the definition I would look that up and so on until I understood using only Japanese.