If you're applying to banks and firms, I think the suiting at Express isn't professional enough. I had looked at suiting there when I was trying to get some interview attire (I ended up getting a Theory suit on sale) and I found the cut of their jackets to not be very professional.
You can definitely wear a skirt suit, but if you're applying for more formal positions you should probably wear nude hose with it (I hate wearing nude hose, so I always wear a pant suit to interviews. And like others mentioned, keep the heels under 3 inches.
If you're 5ft1, you should check out the blog
http://www.extrapetite.com she's a really petite blogger who works in a pretty formal professional environment. She has GREAT tips and most of her wardrobe isn't ultra expensive (I think she shops at Ann Taylor a lot). I think it would give you a lot of good inspiration!