I have this: http://us.suitsupply.com/en_US/coats/grey-overcoat/J245.html?start=15&cgid=Coats which is just the grey version of the one you linked I think. I've had it for only one winter and absolutely love it so far.
I dont have this overcoat but I do have the cashmere version. If this wool one is even half as nice as the cashmere one it will be worth the price.http://us.suitsupply.com/en_US/coats/grey-overcoat/J247.html?start=21&cgid=Coats
I have a SS Napoli and a Classico II both in 36S. I would not say either is more or less generous in the waist or chest. The Napoli shoulders are a bit wider and the trousers I think are slimmer in the Benjamin Classico II.To answer your question, stick with the same size.
Your question is a little confusing (to me) but if I understand it correctly you are asking if this is conservative business dress, business casual or just casual. Which I would reply its just casual, if you're required to wear business casual, this would not be it.
Whats the general consensus on shirt sleeve length? Do you have the sleeve hang from your shoulder to the proper length or is the sleeve stopped by your wrist/hand by the cuff for proper length? In the former scenario if you unbuttoned your cuff it would stay right where it is, in the latter you should have "extra" material such that if you unbuttoned your cuff it would fall further down the hand.