The only universal rule is that there is no universal rule...
Companies, at any stage, are made up of a (semi)random collection of individuals. You can hardly predict their expectations, likes, dislikes, and expectations accurately.
Dress-code wise, I would say dress in whatever YOU feel most comfortable in. When in doubt err on the side of over-dressing, but for almost any "hacker" type role you would never go beyond a sport-coat (possibly with nice jeans and a dress shirt). As someone who has interviewed many people I would say that one thing that seems to negatively affect the dynamics of the interview is when you can tell the person is just not comfortable (and therefore not themself).
Along the lines of not being able to predict how people view your CV, I personally would rather see blank space on a resume instead of blather about what you did in high school or college, which is almost never relevant to what I am interested in. I also personally don't like people who send the followup emails of "It was such a great interview I can totally see myself making a huge contriblahblahblah". Save it, I get enough air-filled emails already, I don't need yours.
Despite what many people might say, there are a LOT of jobs out there. Wear what you want, and handle the process (cover letter, resume, follow-up) however you feel is most appropriate, and iterate rapidly over the feedback (or lack thereof) to adjust your approach.
Personally, I like a brief 2-3 paragraph high-level cover letter that is targeted to the specific job (matches your skills to my requirements) and a resume that is readable and underscores key accomplishments. Dress decent, no matter what position you're interviewing for (if you're at a startup you might have to present to a board or potential customer one day. Having a "nice" set of clothes is a good sign of preparedness, IMO).