As a general rule, I dress casually. I feel like a monkey in a suit. Kind of like most men would feel wearing a kilt, maybe. I didn't grow up in the church, and never dressed up prior to salvation, and part of me felt kind of "fake" when I did so a few times, even when I preached.
Concerning drinking beer, I'm a teetotaler that has the occasional zero alcohol beer because I like a malt beverage. But as for Christians drinking alcohol, I'd say we have been given a mandate for self-control, and alcohol can take that away. We have been commanded to be filled with the Spirit, not drunken. Many will argue, "But I'm just having a little, I'm not getting drunk." The question is, is that true? How much alcohol does it take for our personalities/characters to be affected?
However, it isn't something I view as something to break fellowship over, unless they're getting drunk.
As to whether a glass or two will hurt our witness, for some, probably, for most, not real likely. Can it cause a brother to stumble? Sure. Wouldn't want that on my shoulders.