You are not going to see anything different being an FO until IOE (OE, OJT, whatever u want to call it). Your interview / training will be exactly the same and you will get a P1 type rating as an FO. There is a lot of interview info on this thread...
I believe the BMI is under 30....might be 28. I cant remember for sure. As far as smoking, I dont think there is anyone in our class that smokes, however, it seems that everyone else in Japan does smoke. There might have been 1 or 2 of the Dash or 737 guys that smoked, but I cant remember. Part of the medical is testing your lung capacity so I would imagine that would be more difficult if you are a smoker. If you pass the medical though, I can't imagine it being a problem.
Good Luck