I completely agree with some of your points...but I completely disagree with others. To put it another way, I think I may agree with a lot of what you're saying - but not how you're saying it.
To start with, you're 100% right that he didn't create this world, and us, because he needed us. He is totally independent, and perfect. However, your next step is a bit more vague - yes, he wants us to do good, but it seems to me that that includes the "good" of bein adam l'makom, as well.
You're right - the torah is not a "how to get into heaven" book. But it's also not just a book that tells us how to live in this physical world. I think it's a book that helps clue us in to the spiritual reality, and based on that, yes - it's a "Living On Earth For Dummies" book. It tells us how to live in this world, and get closer to god. Like you said, not for his good, not because he needs it, but for our benefit. But our goal should be doing what Hashem wants.
And yes, we are supposed to follow in his ways, and do good - clearly, that is essential, in so many ways.
BUT - we are also supposed to do things for him that do not relate directly to anyone! For example, not wearing shatnez, keeping kosher, etc. Clearly, we are supposed to be doing these things to build a relationship with hashem. Because that's what HE wants.
i suppose the litmus test of all this is, what happens when our bein adam l'makom and our bein adam l'chaveiro (or at least, how we see it) clash? When halacha tells us to do one thing, but we feel that it's wrong. That the RIGHT thing would be to do something else. That can be an extreme example of "timcheh es zecher amalek," or something more everyday - we can think of a million examples. Or even when a mitzvah of bein adam l'makom clashes with a ben adam l'chaveiro.