Hello, nice to meet you, and welcome to the forums. It's always great to see a fellow Twilight Sparkle fan, hope you have fun here. As for your questions:
1. From my experience they are very nice and helpful.
2. Once you get to five posts, you get the Muffin Rank, at which point you can also post in the Life Advice section. Once you get to 40, you get the rank of Cupcake and can post in the Debate Pit section. The reason for the post minimum is they don't want trolls in those two sections. If you want to see the full list of ranks, check out this post.
3. In general, just don't be a jerk.
4. Yes that's fine, as long as it's relevant to the topic. When you post a video link like a Youtube video, it should come up as the actual video instead of text.
5. Sorry I don't. But there are a lot of people on here always looking for other people to read theirs, so check that out if you want.
Like I said, welcome to the forums, I hope you have a good time here.