Looks like some of the other members have already answered most of your questions with some very good information but I'll throw in a couple of things.
1. Tank size- I use the one inch per gallon rule of thumb when stocking my tropical tanks. As a rule this keeps the bio load light and gives your fish more room to roam as well as grow. I keep a 20 gal tank right now for my trops with 6 Corys.
2. Water- With most individuals of this species, water properties are not critical. Most thrive in water with a pH level of 6.0-8.0, a hardness of 2-25 dH, and a temperature of 72-82 degrees F (22-28 degrees C). I keep my pH levels at 6.8-7.0.
3. Food- Live foods such as aquatic insects, white worms, tubifex, brine shrimp,insect larvae, wafers, pellets, and flakes.
4. Substrate- As long as the gravel is rounded with no sharp edges it should be fine. Gravel with sharp edges will damage the barbels. Fine sand usually is your best bet which encourages their foraging ability.
5. Group size- Hidr told me that Corys thrive in groups of 6 or more which I agree with through my own experience. Although the group of 6 doesn't necessarily have to be all of the same species, I recommend at least 2 of each as all Corys get along fine with never any aggression towards other species. They will do well in a group of 2-3 however I've found the larger the group the more activity you'll see in your Corys. Good hiding places as well as a larger group atmosphere will certainly eliminate stress as well and actually promote breeding activity.
6. Planet Catfish- Kristi hooked me up with this site which I feel is the best Cory Cat info site out there as well as having it's own forum. Descriptions and photos of all species of Corys make this site second to none concerning Cory Cats. Tons of info for anything that you may need.
Hope that helps!