I don't think studying the Chinese language first will help you much in learning Japanese. It'll make it easier to learn Japanese kanjis, but it wont help you much in learning words. Basically, kanji is about the only thing that's similar between those two languages, so you should just focus on learning Japanese. Before you try figuring out the easiest way of learning Japanese, do you first have an idea of what skill you want best? Is it reading, listening, speaking, or writing? Knowing your priorities first will help since maybe you don't want to read that much at all or maybe you just want to focus on reading.
Anyways, no matter what your choice, I think it's still best to learn hiragana and katakana first. This way, more textbooks will be available to you.
After you learn those two things, try focusing on learning vocab. You should try a flashcard program in order to learn it, but not just any. Pick a flash card program that's a spaced repetition system (srs) such as anki or mnemosyne. These programs are great for learning Japanese easier because you get to score how well you know a card from 1-4 or somewhere around there. And based on your scorings, cards you know easier will be shown to you much later than the cards that you find more difficult.
To get basic grammar down, either get a textbook so that you'll have a structure to fall back on. For instance, Genki, it's a textbook that's often used in universities. If your self-studying, try Japanese for Everyone, not only is it much cheaper, but it provides answer to the exercises at the back of the book. You can also go to an online site, like Tae Kim's Japanese Grammar.
If I knew more about your interests, perhaps I can give you more specific ideas.