1. The speed should be the speed you need to get down the lines evenly and be carried out consistently throughout the course, unless instructed otherwise (for instance a hand-gallop jump). Generally speed has a lot to do with the stride length of the specific horse. A horse with a lot of step may need to go slowly to retain the relaxed hunter jump which is preferred and the required number in the line. Smaller horses may have to "go" a little bit more to make it down the lines. Classic hunter classes are all about making it look easy and effortless.
2. It's really not about the lead change, technically when you trot to change your lead you're technically breaking stride, which does knock down your score (quite a bit). It's basically counted the same way as if a horse randomly broke to a trot in the middle of the course. https://docs.google.com/viewer?a=v&q...JHgbaOY8DWK0Hg
This is for paints, but score sheet is very similar to how open hunters are scored as well.
3. Typically in corners you want to use as much ring as possible, while making the rounded, rather than sharp. Typically more round turns look more relaxed and less frantic.
4. The first round is scored like a classic hunter round. They want a horse that moves nicely and jumps round and square, while maintaining a nice hunter expression. Typically horses are rode more boldly through the course, but consistance of speed is still needed. The course is longer (10+ jumps) and adds different elements not seen in typical rounds, at least, not seen together. This includes in and outs, bending lines, lines that don't measure perfectly, and natural elements, often times you're ask to jump in or out of the ring
5. It's not suppose to, but many people will still wear a coat and you typically want to be with the majority. If nobody else is wearing a coat then go for it, but you don't want to be the only one without one. For equitation class, I would always wear a coat unless it's a health risk. It just looks much more put together and if it comes down to a tie, the one that looks more polished will probably come out on top.