For shot 12, I think it's better to use wide open to improve the bokeh, since you are close to wide open at f2.8.
Thanks for the advice. I was thinking f2.8 may retain some of the lens sharpness. BTW, i will try taking same photo with different Aperture setting. Those are for the condolence and wishes for the Sewol Ferry accident victims. I had no idea whats on those Korean characters, except of of them was Chinese.
Ah, this is the old 35/2, very recognizable due to its pentagon bokeh. Which I think is quite sharp even wide open, so yeah I agree with Chai, better to open up to f/2 to keep the bokeh rounded and smooth.