Hiya. I'm still fairly new (2 weeks ish), feeling my way around. Don't know the answers to all of your questions, but...
1: that's your reputation score. It starts at 25 and grows. I don't know whether upvotes or comments or resteems increase it, but it goes up. It can also come down if you get flagged for things. Flags are supposed to be there to report abuse but I've seen evidence of them being used maliciously.
5: I've seen people upvote the original post a small amount, then upvote their own comment loads. When you've been here a while and gained power, you can choose the value of your vote. It strikes me as cheating. Of course we are gonna like what we say; it goes without saying, without having to pin a medal on our own chest. I find it off putting but some people are fine with it, apparently :)
7: don't piss off any whales.
Thank you!