I would say that the expressions are correct, the way that Pinkie and Rainbow Dash come in work because 1. Rainbow is a pegasus, and 2. Pinkie can break physics. I would say, if anything the faces need a little bit of work, RD's face looks a little scrunched up in the center, and Twilight's eye seems a little too big. The eye thing is probably just me. But Pinkie Pie is correct for the most part. It also feels very Calvin and Hobbes, which I love. Overall, very good work, and hope to see more of the same from you.
It's up. I don't think the railing gets a shadow simply due to the simplicity of the animation style. I took a bit of liberty and did a blended shadow instead of flat, so it "fades" instead of having an edge.