They are difficult, I sold a "most likely pullet" which turned out to be a boy. I also bought a three month old pullet, which turned out to be a boy. They are not an easy breed to sex. Good luck.
My last hatch was a few weeks ago and I'm greedily hanging on to them, crele orpingtons!
DH has been trying to convince me to put a (literally) two gallon bucket full of eggs into the incubator. We just moved 98 chicks out of the brooders and into the first stage indoor pen. Most of them are big enough they could be thrown in with their parents.
NO CHICKS!!!