First, it depends on what you mean by the astral plane or astral projection. Some people think that lucid dreaming counts. Others think that only out of body experiences count. I used to be in the latter, thinking that Pathworking meditations were useless, and now I think they're more useful than out of body experiences.
1) What should I expect to see in the Astral Plane?
Release expectation. You might have astral vision trouble. You might be able to see all eight corners of a room at once. You might have seen something, or feel like you saw something, but be unable to remember it when you get back. Or you might see anything and remember all of it just fine.
2) What can I do in the Astral Plane?
You'll never know until you try.
3) How do I get back to my body once I project?
That's automatic. It can even be annoying if you want to stay out for longer. A full bladder, an empty stomach, or just remembering that you have a physical body can pull you back.
4) How long does it normally take for someone to first project?
It took me 3 years to figure out how to do it, then it only took 20 minutes. The strange thing is, it didn't feel like I got better with practice. I figured it out by accident. Then, I realized that I could have accomplished it within 20 minutes of my first meditation attempt three years ago, if only I already knew what I was supposed to do! I had read the explanations of what you're "supposed to" do, and they were all true, but it's not something I could understand from having it be explained to me. That is exactly as annoying as it sounds.