Having a reference is helpful and to keep you from accidentally tearing into the membrane where it is against the shell. The chick has to pip through the membrane but you can get a better idea of the condition of the membrane through the air cell without the danger of tearing a vessel.
The first thing to do tomorrow is to candle and circle the air cell with a pencil. There is a lining inside of the shell but the membrane will be against the chick, that is the one that will have the blood vessels.
When the beak is outside the shell and can not be retracted, it can not chip the shell. This is caused from too high of humidity and the chick didn't lose enough moisture and is crowded in the shell. It is very iffy being able to tell when it is too early but if you carefully chip a small bit...
If the chick can not pull its head back in to continue zipping it will not be able to hatch without help. The egg did not lose enough moisture and the chick is too big without enough room to swing its head to chip out. Either your humidity was too high or the shell was not porous enough to let...
Mites are very unlikely, however, lice could be a problem. We have never had any lice on chicks that young but if they were with a broody in an unclean environment it could be possible. Personally, I wouldn't worry unless you actually see the lice on the bird. Once the chicks go on the ground...
Pea eggs are one of the most difficult eggs to hatch, and being shipped makes it even harder. Shipping will lower the number of eggs that will develop because of the rough handling and vibration they endure in transit. To be successful you are going to need to know how to observe the internal...
No, not enough distinguishable markers to tell you plus it is a bit early. When asking for sex, a pic of the whole chick from front, side, and top really helps.