If I were approaching this broody issue, I would go in one of two directions -- either get a breed that is frequently, annoyingly broody to do a very specific job within the flock and not worry about its other skills, or I would get a breed that I really like in general and search out a particularly broody strain. (There can be quite a difference between lines and between individuals within the same breed. I have seven Barnevelder hens from the same line. Five have never gone broody. One goes broody like an average broody hen, but will maintain the brood for months if nothing hatches and I don't break her brood. One goes broody with such a deep trance that she has to be tube fed daily or she will die of dehydration before she starves to death, and does not come out of the trance at all unless I rub ice cubes on her cheeks, which I need to do to get her to stand up and poop, as no amount of harassment, including tube feeding, will wake her up. She will maintain that depth of brood for months if I didn't break her brood -- she is actually the reason I've gotten so efficient at breaking broods, as she is quite stubborn, and goes broody quite frequently.)
Or you could get Dorkings, which have all the qualities that you're looking for, but I may be a bit nearsighted about my favorite breed!
I thought I'd settled on a breed and was set to begin further research into breeders, lines, etc but I've come back to this over and over again and I'm seriously questioning what are important traits for my flock and how to accomplish it with just a single breed ......you've got me thinking Sydney Acres!!
Cheers

M