3 weeks is a bit young to be able to sex SFH, or a bit old, depending on how you look at it. Some people have good luck feather sexing them at 3 days old. You can try posting pics (good side head shots) when your birds get to be 6-7 weeks old and we will try to give you our best guesses, but lots of times that's exactly what they are at that point - guesses. The crested ones can take longer to be sure. Usually by 10-11 weeks you will know on all of them. What you want to be looking for is definite wattles coming down - the pullets don't get wattles (more than a sliver) until they are getting close to POL. also, on the crested ones, roos will have spiky crests and the pullets crest feathers will be more rounded. I hope this helps.
thanks KYtinpusher. I appreciate your help. Will wait & post pics at a later date.