ok i opted out of doing the fishless cycle...i set up my tank and read up on some good "hardy" fish to cycle. I went to petco and got 3 gold zebra danios and 1 painted platy. They are doing fine so far, but I noticed one of the danios is much larger than the other two, which i've read indicates that it might be female. If that is the case how will i know if she lays eggs? and what do i do if she does??

If the female is pregnant, her belly will begin to swell to the size that it is definitely noticeable. The older the fish, the more babies she can have and therefore the size depends on how old she is. It will be harder to tell on a young female. You will probably need to get a breeder to put the female in because the other fish will eat the eggs.