Wow, from the front that looks like a great fit for a thrift. No vents makes the coat more formal, though also a bit less comfortable. Yes, take the sleeves up to your wrist bone.
The lapels have a nice belly, and the high but tasteful gorge ensures that it doesn't have the pouter-pigeon chest of 80s DB drape cuts.
It looks good on you, because you're trim and not barrel-chested. I'd consider moving the four show buttons in by half an inch or so. This will lengthen the line a bit and make the coat a bit less conspicuous and chest-obsessed. Check out what close-set show buttons do for Astaire on his 6x1
. Notice that his top show buttons almost touch the lapels: looks great on him. Your torso seems to have roughly the same shape as his, so I think it'd look great on you too.
If you want to make the coat slightly less conspicuous, silver-toned buttons are an option.
All in all, very nice. A classic DB. I wish I had one like that! Wear it with pride! You'll be helping put to rest the myth that 6x1 can't look good.
I wrote a bit about their history here