You don't have to invest in a teacher. I mean, this website is a great tool when you have doubts or questions! You can ask them, get answers. Or even get in contact with native Japanese people.

I all depend on the person. I hope you receive the answer from thevlearners who have already had classes with professional teachers. For the first step, in my opinion, accept all the Japanese translations for simple sentences and repeating them again and again without thinking many things would be one of the good ways of learning. I did so when I started learning other languages. Because our languages are totally different and sometimes understanding the meaning of each word is impossible. (Ex: I am Australian / I am at home / I am going to buy a book / etc, these "am" aren't the same in Japanese.) Anyway, good luck to you.