Thanks guys -- I have returned from the dealer with news (or not news, depending upon your perspective).
1. oil change -- at 2,500 miles, I decided to do the oil change anyway. I looked at the car on the rack as it was being done. The fluid did come out a little dark but was still fully serviceable. I don't regret doing it ($85) but it probably could have waited until 5K. I will probably get it done yearly (or 10K) at this point. I know there is a lot of talk on the subject and people disagree but i'm planning on keeping a while.
2. As suspected, the tail pipe soot is "normal" and expected during the early part of the car's life. The youngish mechanic tells me that all of the exhaust components have protective coatings that will burn off in the early stages. He told me this should dissipate over time and is perfectly normal. Okay!
3. Speedometer -- this is ALSO normal. They printed out a service bulletin (I can give the number to anyone who wants it) that described the exact condition I was describing. They say most new cars do slightly overestimate the speed by as much as 5%. Interestingly, this does NOT affect the odometer which records miles digitally (not sure I understand where it is getting its data if not from the same source as the speedometer). So, once again, normal.
Thank you, everyone, who took the time to offer your 2 cents. I feel more informed now and maybe feel a little more confident that my car is being taken care of diligently.