Breeding lights with buffs is very common. Some buff breeders use a light hen to increase the size of their buffs. Leakage is seen during the f1 cross in males, females will look like the roosters used. If you want only lights pick the ones with the best type (wide, wide, wide) and try to use...
I hope yours are friendly, my hatchery cochin was the meanest bird ever, came at us feet first. I look to see if I can find his picture. He was beautiful and I love his girls but all boys from him were mean. This was before I got into exhibition birds.
Feed store chickens will not meet the standards of Exhibition birds. I have found the hatchery birds to be normal size not much bigger than a rhode island red. The main difference will be the comb, they body types are otherwise similar from hatcheries. Hatcheries breed for quantity not...
Silly birds, you can ask on the Facebook site, but most heritage breeders don't sell eggs. Those that do will do it usually at the end of the breeding season
Go to the American brahma club on Facebook that's where most of your great breeders are and many are willing to ship birds. I had to have mine shipped from out of state as there were no breeders in my area.
The base color comes from the male but leakage (extended black) comes from both. Structure comes from both. Type it is very important to brahmas. Wide, wide, wide. Wide head, wide body, wide tail (inverted U). It will take many years to get the body type you want if the original hens don't...