What would I have done differently? One size larger.
My measurements:
Size of FO:

2015-03-02 Got gauge with the 3,75 mm needles. Starting to knit.

2015-03-16 One sleeve finished, front side finished. It’s a pretty quick knit. 5 skeins is way too much yarn, I guess I’ll need 4. My stash just keeps growing :-/

2015-03-23 Blocked two sleeves at the same time. It worked great!
To get the measures right, I drew up the pieces on parchment paper and blocked the pieces using the drawing. Worked like a charm.

2015-04-06 Finished! Almost everything done by the book.
Mods: I’m only using 4 buttons. And I’m wearing it with the placket on the front. And I don’t intend on button it up, ever! I also added some crochet edging: on the sleeves, at the bottom and on the neckband. Each one different, each one simple (two rows of crochet: the first made up of chains and SC to establish the Foundation for the second row, where I worked sometimes simple picots, sometimes picots between HDC and DC stitches).

Got already some great compliments ;)