Mine is an adult, but still quite active. He has a large enclosure, but I make sure he gets out at least once a day. You will need to be very gentle with a baby.
For a pet, I would just go by tail length for sexing. Soderberg's book has tail photos for reference, if you haven't already found some on-line.
Preventing escape is probably your biggest worry while the snake is tiny. They are VERY good at it.