As long as they have been in a tank with males in the last couple months, you will get fry. Just keep in mind that it only takes a very short time until you will literally be over run with fry. with 3 females, in about 3 months, you will have 500+ fish. I wouldn't put them in anything less than 5 gallons though. They need swimming room.
As for the tank size you mentioned in your original post, get the biggest tank you can afford and have room for. It opens up so many more options as to what type and how many fish you can get. Larger tanks are generally much more stable too as to the water parameters.