Interview clothes help

I need to go to a job interview and am not sure exactly what to wear. This is for a summer job for fun after college (I am 22) at the mens clothing department of a major upscale department store. I am conflicted between dressing as conservatively as possible and dressing with a flair that shows I understand and am comfortable with the finer points of style.

I only have one suit at the moment, a Brooks two-piece flannel chalk stripe, so there really aren't any other options for suits. But I don't know whether to pair it with my rather aged Church's black cap-toe oxfords or my newer brown cordovan cap-toes.

I am thinking a white shirt and repp tie would be best, and a pocket square is a must. What do you think?