I just spent a month in Rome studying, and I can definitely endorse Tazza d'Oro. Best coffee for sure. And the apple croissants at San Eustachio were a huge hit with all my friends. However, they do tend to run out rather early in the mornings.
As for gelato, I recommend Frigidarium near Piazza Navona. Everybody else says San Crispino has the best gelato, but I didn't think it was all that special. Plus, it was more expensive than most everywhere else and just oozed pretentiousness.
As for actual meals, I don't know about the places you listed, but if you're in the mood for pizza nothing beats Pizzeria da Baffetto, which is right next door to Frigidarium. At around 8 or 8:30, a line starts forming outside, so get there early or you'll be waiting a while. Seriously, they don't make pizza like that in the US (or elsewhere in Rome, from my own experience).