Wait a few more weeks, the organs are still growing. At this stage, bucks will look like does. You will have "sex changes" as many breeders call it if you try to soon. Wait and enjoy ... worry about gender later!
Most breeders can sex at 4 weeks, but it's easier at 6 weeks. At 4, you will get some surprises - it's not 100% accurate.
As to seperating bucks and does - you can keep the weaned litter together for a while. For breeding - you are probably safe until about 4 months. They will be some dominance (chasing and humping) and fur chewing problems after about 8-12 weeks.
At about 4 weeks of age, if you can tell the difference between a "1" and a "0" (the "1" will be a female). Hold the rabbit by the skin just back of it's neck , place it on it's rump, place two fingers on eather side of the genitalia and gently press downwards. You will then see an "1" or an "0".