If you're interested in the program, you hopefully want public health to be a major part of your long-term career plans, make sure that comes through in your statement. I applied in 2013, so I'm not sure if they'll change the prompt or not by now.
1) Nah, as long as you're going to graduate you'll be good. I think you have to have the registrar fill out a form... I could be remembering this wrong, but get it to the office so they can complete it quick.
2) It's long, drawn out, and a good intro to being patient while working for a large govt agency. Be patient with it and be genuine about your long-term plans and interest in public health.
Also, if someone starts a 2016 thread, put it in a comment below and I'll try to pop in to answer questions every once in a while.