Some yoka tips:
This is just what I've learned about my yokas, and may not apply to all yokohamas.
They do not travel well when shipped with other standard chicks. Although they are considered a standard breed, they are much smaller than the rest. Only 1/3 of the yoka chicks that were shipped to me from efowl ended up surviving (not to detract from efowl).
If you're buying the red shouldered variety, aim for as much red on the chest as possible. Little to no red on the chest will be a larger fault than too much red, and chances are you could get that perfect patterning.
Feed the hens extra protein. I give them non-medicated chick feed, with 18% protein. I've found literature talking about how they only lay one egg a week, but even before the extra protein they were laying about once every other day.
Don't keep yourself from buying the perfect bird! Remember, this is a critically endangered breed. Expect prices to be in the $30's and $40's range for an adult yoka, especially one of breeding age. If you're not ready to pay that price, the chicks are much cheaper but they are rather fragile from what I've found, so be careful with whom you buy them from and what other chick breeds they are being shipped with or raised with.