In general, males have longer fins than females. However, there are some fin varieties (plakat, halfmoon plakat) in which males have short fins. The one sure way to tell is to check out the ventral fins (the two fins that hang down). If they are long and thick it's a male. If they are short and stubby, it is a female. If you can get him or her to flare, see how he or she flares. Males flare sideways to look bigger, and females flare facing their reflection.
As for cycling, http://www.fishlore.com/NitrogenCycle.htm has great information. :) When it comes time to stock it, you could have a variety. Cory cats can be kept in groups of 4 or more along with eaither tetras (they need about 6 or more but do very very well in the bigger tanks) or platies (you just need a ratio of 2 females to one male or all one gender). :)