I'll throw out my opinion. Take it for what it is worth.
That surprised me a bit. According to Henderson Breed Chart, New Hampshires can be broody. I thought since they were derived from RIR they would not be. I know, strain is important.
http://www.ithaca.edu/staff/jhenderson/chooks/chooks.html
I think you just take pot luck with hatcheries. They are probably going to be pretty good layers since their breeding flocks are there to lay eggs for incubators. I think broodiness is a little more problematic. Their flocks are to lay eggs for incubators, not to hatch the eggs themselves. That said, my Australorps from Cackle go broody. Size is something else that is problematic. The hatchery breeding stock is not selected for size. They select for egg laying ability that pretty much (certainly not to show standards) conform to color, configuration, comb, skin color, and other traits of the breed. Note I said pretty much, not that they are rigorous in that selection.
I think you also take pot luck with breeders. Some people raise from hatchery stock and call themselves breeders, althoughg they are not real good as selecting for the standards of perfection. If they are honest about that, I have no problem with that. Some people that call themselves breeders are dishonest. That is a risk you take. Not all breeders that know what they are doing and are honest select for the traits you want. The advantage to buying from a breeder is that you can talk to them about what traits they are breeding for. Many will be honest and tell you whether or not their strain will meet your needs. I think a big advantage of buying from a breeder is that most of them are passionate about what they are doing and really care about their birds. By talking to them you can often tell which is which.
I think with the traits you are looking for, you can buy from a hatchery and get a flock as good as most backyard flocks were 50 years ago. They should lay pretty well, they will get big enough to eat, and, well, not all our backyard flock went broody every year. You really only need a few.
If you can find a breeder that breeds for the traits you want, you will be better off going to them. I want to be pretty clear on that. The better stock you get to start with, the better your flock will be. But for your goals, a hatchery is probably good enough.