A trio is about all you'll have space for in a 5 gallon. You will want at least 2 females per male since some males can be so amorous that they can actually stress a female to death with constant breeding attempts if they arent given more options. You will also need a tank for the fry to grow in, at least 5-10 gallons since fry drops can be as many as 50 or more for a mature female. Fry should get water changes at least twice weekly and fed multiple times per day. I put mom in either a breeder net or birthing tank so that the dads dont eat the fry or try to breed with her while she's giving birth. If you are serious about breeding quality guppies to sell, you should have 3 fry tanks. One for very young and unsexable fry, and one for each gender as they become sexable. Then, as the fry age, you should "cull" ones with inferior attributes. Culling can either be euthanizing, which I dont like to do, or giving them away or selling them to pet stores. Dont sell your culls to customers expecting high quality fish or you will not have a good reputation and people wont want to buy your guppies. Since your adult tank is so small, you should make sure you have a market of homes for the fry as they age, otherwise you will be very quickly overrun. Females can give birth every 28 days and it takes a good 3 months for guppies to reach a sellable size. Consider then, you needing to house 150 or more guppy fry at a time. You may not get drops this large, but it is better to be prepared than completely overstocked.
Breeding guppies is easy. Being a quality guppy breeder isnt. It IS fun though, so good luck!
