First of all, let me clarify my Brooks Brothers recommendation. It’s great if you have money to burn, but if you don’t, look for something more price-competitive.
Second, Joseph’s guidance is good, but it needs this caveat: The suit should fit, the shirt should be tucked in, and when it rains, do not put a plastic bag on your black hat to protect it. Black felt is naturally water-resistant and will be fine when the rain stops. You will not learn this by observing the bochurim going in and out of yeshivas.
Halachic question: How disheveled does a bochur have to be to be committing a sin against the Halachic dress code?