That should be a good number to give you a variety of personality types of
both genders of that breed and a decent starting point for anyone really.
Wyandotte are great table birds, have their share of broody behavior, and are fairly hardy even in addition to being lovely!
Getting a variety to see what works for your family is a fantastic idea!
I just noticed I'm replying to two different posters.. I think my answer is still solid... mostly... you mean you wan't to order 15 birds with 8 being sexed pullets of other breeds and 7 being straight run Bielefelder??
That would give you 3 - 4 roosters/cockerels and 11 - 12 pullet/hens if I'm understanding your question correctly. That would very likely be an out of whack ratio long term and you would want to have a plan B for your extra boys.
Cackle is a fine hatchery with a reputation to protect and they will NOT purposely send you 7 cockerels if you order straight run Bielefelder from them as that would be unprofessional and in this day and age of social media and internet access could seriously harm their livelihood. Most folks who do
good business make SOME money while providing products or services... over the long term... earning repeat and new business in order to protect their families. I promise you as someone who sells my birds for top dollar... it is NOT a get rich quick scheme... Gathering, breeding, maintaining flocks and facilities... it's a labor of love. Some birds are not easy to find and that is why they cost more than the very common ones... It literally took me several years to find and acquire my bantam Ameraucana breeding stock and several multi hundred dollar investments... plus my actual time... You really do get what you pay for, very often... They're offering a steal... and I'm not a plant nor do I work for them or get any compensation besides being a passionate BYC poultry keeper helping my fellow chicken keeper get what they want and enjoy it too!
Sorry, emo day.