My two cents:
Do be careful not to get too many males compared to the number of females. If you have too many males, especially guppies, the males will always (or so it seems) to be chasing the female. Not having a moments quiet can stress the fish out quite quickly. 50/50 is a good mix of males/females.
Also, do not assume that because you're getting a female that they will breed (if that's what you're looking for). Males and females will choose their own mates. If the ones available aren't suitable, they won't breed. They can also become quite attached. I had a male and female (breeding pair) of swords and the male died. The female committed suicide by jumping out of the tank through a one inch square opening to provide fresh air circulation. While swords are jumpers, she had never tried to jump before the male died. It was my poor luck that she jumped while I was at work and I could not save her. I've been unsuccessful since in breeding them.
I'm firm - but fair. Mind the rules and enjoy your stay.
According to the Humane Society of the United States:
There are an estimated 3-4 million dogs and cats euthanized each year in the US alone! PLEASE - spay and/or neuter your pets!