I'd just take the females back and use the 10 gallon for an all male tank personally. As long as the filter has a good sized sponge it shoud cycle a tank with that low of a bioload. I have two guppy tanks with small box filters that are cycled, and a box filter is about as little filtration you can get.I've never heard of taking the rocks out. The more hiding places the better. The mother will turn around and eat the babies as well as every other fish in there will.