I keep guppies, but they aren't the fancy types. Mine are in a 10 gallon that's kept around 75-78 F.
For them to stay healthy and active a higher ph is better. My ph is 7.0 and they are doing fine but they prefer it around 7.8 or so

Don't keep them with fish that will nip their fins (if you get the long-finned guppies)

I heard they should not be kept with bettas either.
As everybody else said, it's best to get males if you don't want babies. The last female I bought was pregnant and I didn't know it until I seen the fry swimming! LoL
Good luck!