If I set a few eggs, not knowing if they were Barred Rock, Rhode Island Red, or Black Australorp, would I be able to tell what breed they came from based on chick characteristics or would I have to wait for feathers to come in? I can't keep them all, so if I could pick and choose who to grow out and who to sell early on would be best. I'm supposed to be breeding silkies, this would just be an interesting rabbit hole
For that rooster, with hens that are Barred Rock, Rhode Island Red, and Black Australorp:
I'm not sure what you will get from the Rhode Island Red. They have mostly recessive genes, so the chicks will mostly show whatever they get from their father. If you get any chicks that are red or gold in color, or have chipmunk stripes, they will definitely be from the Rhode Island Reds, not from Black Australorp or Barred Rock mothers. (But some chicks from the RIR mothers may show the same colors as chicks from any other mothers, depending on what that rooster has genetically.)
For the Barred Rocks: sons will have the gene for white barring, daughters will not. On black chicks, this shows up as a light dot on the head of males but not females. It also shows up as they start growing feathers, within the first few days & weeks. For any chicks that inherit a gene that makes black into something lighter, the dot will not be as obvious, and you might or might not be able to see it (this applies to blue/splash, paint, chocolate, khaki/dun, and so forth.)
So any black chicks with a light dot on their head must be sons of Barred Rock hens. You could sell them early on, knowing they are males.
Black Australorp chicks, both male and female, will have the same set of coloring options as daughters of the Barred Rocks. The chicks should be black (genetically speaking), with the black then maybe being affected by whatever the male has (paint, chocolate, or whatever is going on.)
If it were me trying to test that rooster, I would probably count the chicks of each color, then sell any that show:
--coloring like a normal Barred Rock chick (black with yellow underneath, and yellow dot on head). These are males, so be careful that the buyer knows that.
--any red/gold/chipmunk colored chicks (these have the Rhode Island Red mother)
--if there are still too many chicks, any that look like normal Black chicks (black on top with yellow underneath, a bit like a penguin).
At that point, the remaining chicks could still have any of the mothers, but will mostly be the ones that are interesting for figuring out what the male has.
If the various eggs look somewhat different, even if you don't know which hen lays which eggs, you could have them hatch in mesh bags or little baskets, and then mark the chicks according to which group they came from. After they hatch, you might be able to spot which mother produced some of the chicks in a group, and that could tell you the mother of that whole group. But if they all lay eggs that look fairly similar, then obviously this idea won't do any good.