I agree with EMS here but I think you might even be safe with 6 females and 2 males and then let nature take its course.
You will want to have plenty of cover for them, such as live plants and drift wood.
I love having Hornwort and Java Fern in my tanks. These plants will give plenty of spaces and areas for the fry to hide. Also the plants will have infusia (small tiny critters) that the fry will eat. This is a great bonus. Also if you want to have an algae eater in your tank, besides your guppies. Yes, they do eat Algae and are very good at it as well. I keep Amano shrimp in my tanks. I do not have to worry about them getting to big to bully the fish and they do a bang up job eating the stuff.
Never use a breeder net or those small breeder tanks. These will cause to many problems and will cause either the death of the female or abortion of fry. And as EMS said, they will breed for you. Remember to do regular water changes, every week. I usually make sure I do one on Saturday Morning for all my tanks.
