It's really not a big deal, and you don't need to dress like it is (depending on the country of the visa and your own nationality, of course - sadly, it is much harder for Middle-Eastern/Pakistani men to get visas granted). Mine was over in under 60 seconds, kid you not, and I don't know if I would've survived that hellishly long line in a suit.
it depends. wear something you're comfortable in. but dont wear sleeveless or shorts. i wore a collared dress with sleeves. the guy before me was in a suit and he kinda looked sketchy because it made him look over eager since everyone around him was just wearing smart casual attire.
