No tail feathers are roos.... Hens develop all their feathers more quickly. If you band them now you will see. Wellies get very substantial legs so make sure to check fit and change out the bands as they grow.
Zip ties work....
This has been accurate for me in my very small previous sample. With my current group, 5/6 have very developed tail feathers at 3 weeks. I'm curious to see if that will be the case. I don't see many other traits yet though