Use your suit for interviewing only. Have it dry cleaned only when necessary. Excessive dry cleaning can prematurely wear out your suit. A cheap department store suit will look cheap and wear out quickly. You should go to a good men's store for advice on how to look for quality clothing and proper fit, even if you don't buy a suit from them.
Advice is free.
You should polish your shoes as well. This is the easiest decision. Everything goes with a white shirt. There's no hassle trying to guess what suit or tie looks best. If you don't like button-down shirts, you should get a straight collar shirt.