Well, you have more fish than I would have put in there.
When stocking a tank, you need to consider adult size. Find out the adult sizes of fish you want before you ever buy them. Then you can make an educated decision before you are stuck with them already in your tank. Fish stores typically sell juveniles because it makes good business sense for them to sell fish before they reach adult size. Thus the fish should get bigger than when you buy them... sometimes MUCH bigger. Also some fish require a lot more space than others because of their activity levels. If I were you, I would find out how big the fish you already have should get, as well as if any have special requirements, before delving in to buy still more fish.
Popular stocking requirements are one inch of fish per gallon of water, or one inch of fish per 10-12 square inches of surface area of the tank (length x width). However keep in mind that one full-grown 12" pleco will put out a lot more waste than a school of 8 1-1/2 inch cardinals, even though they are both technically 12 inches of fish.