1. Format. This depends on the journal. Any journal should provide LaTeX and Word templates for their preferred style. It may not be necessary to use them for the initial submission — check their author guidelines and do exactly what they say. It doesn't matter what you think of their style: their journal, their rules. When you want something from someone, do not give them reasons to say no.
2. Yes: you have to write the paper. Get other people to read it and tell you how bad it is. Give presentations of it and field hostile questions. It builds character.
3. Different institutions may have their own rules about author order. A frequent convention is that major contributors go first, the head of the research group goes last, and everyone else is in the middle. Alphabetical order for ties.
4. You can only submit a paper to one place at a time. Multiple submission is pretty much never acceptable. If detected it may be grounds for instant rejection. You can also only publish it once. A further paper must be a sufficient advance on previous work.
5. The journal editor sometimes makes the decision himself, without sending it out. When he turns it down, this is called a "desk rejection", because it never gets past the editor's desk. That aside, anonymous peer review is the way it's done almost everywhere, although it is lately a subject of some contention. Sometimes it's doubly anonymous: the reviewers don't know who the authors are, although realistically, it is often not difficult to guess.
6. I haven't encountered conference-journals, but there does exist the opposite: the authors of the best papers at a conference (as judged by the conference committee) may be invited to brush them up for publication (usually with peer review) in a special issue of a journal.
7. Mm, not getting into that one, beyond mentioning public-access journals like the PLoS family. Beware, however, of predatory journals and conferences that accept everything for a fee, even randomly generated nonsense, but which nobody reads. Subscription journals aren't the only rent-seekers around.
8. Arxiv: Yes. Also biorXiv for biological sciences. There is some small hurdle to pass, I forget exactly what. In physics, I've heard, everyone reads arXiv to keep up, and eventual journal publication is just a formal stamp of approval that the experts don't need to see because they're the ones who gave it that stamp. For junk and crackpottery that can't even get into arXiv, there is viXra, which is only technically publishing, i.e. anyone can read it but nobody will.
9. Sci-hub: Yes. Well, exactly who is committing an offence and in what jurisdiction I'll leave to the lawyers. BTW, it's worth just googling the title of a paper, because you can often find a copy put online by the author, maybe a pre-publication version. You can also ask the author directly for a copy. They will usually be happy to do so. Also, not all journals are paywalled, e.g. PLoS, and some journals publish a mixture of open and paywalled articles.
10. Value of publishing: In the general sense of making your work public, yes, or why are you doing it? (Well, maybe to make money from your discoveries, which you don't want to reveal until you've made a huge pile, but that's not the usual way things go.) Putting it in a journal or on arXiv gives it permanence and a standard way to refer to it which you won't get by putting it on your blog. As for prestige, except for academic promotion committees who just add up the impact factors of the journals you've published in, the prestige comes from the work, not the venue. The most that the venue can do for you is bring the work to more people's attention. After that, the venue no longer matters.