My company is somewhat larger and older than your target, but probably still similar. When deciding who to interview I don't even read the cover letter (if any). Instead I just skim through the resume and if the candidate seems to have some sort of reasonable software development background then I'll arrange a phone screening interview. The phone screen is where I make the decision about who to bring in for a real interview. If the candidate turns out to be completely unqualified then I can cut it off after a few minutes, no great loss.

As far attire, it's also irrelevant to me. Just don't show up in anything wildly inappropriate.