I would help it out of the shell just leave a little bit, after you get it out of the shell make sure the chick stays warm. I've had to do it before with my ducklings it works
It looks like a cockerel because of how young he is with a comb that big. I'm pretty sure it's a cockerel. I got two cockerel with big combs at 3 weeks old.
I can answer number 4 for you: you should get two females so that way he doesn't over mate with the one female. A khaki wouldn't be to big, I've had a khaki female and a Male mallard I ended up with babys from them.