Determining Gender / Transplanting

My babies are four weeks old [from seed]. I currently have 14 in one gallon pots and I’d like to transplant six of them into five gallon pots to flower.

I have two questions: First, how can I tell which ones are female so I can make my selections? I don’t think I’ll have enough room to flower all of them – I might have to give away the “rejects” - so it’s important that I get it right the first time. Also, at what point should I transplant them into five gallon pots? The tallest one is 10” right now.

Thanks in advance for any responses!