no no no DONT do convicts, to small a tank, same with swordtails, to small a tank. guppys woould be your best bet, male convicts can grow to excede 5 to 6 inches female 3 to 4 inches, swordtails can grow to be 4 inches ( excludeing the sword part on males ) with the sword then about 5 inches for male swordtails, so guppys are your best bet.
2 males 8 females and watch the baby population BLOOM