Hi,
my one and only Sussex is constantly broody ( she is sitting on a cluch due on Fri as I type) she only manages to lay for a couple of weeks at a time and then she's at it again. She started being broody soon after she came into lay so I have never really had a good laying period from her. Having said that she is an excelent mother and will raise healthy chicks through all weathers.
I know Sussex have a reputation for being good broodies though not all will be as obsessed as my little hen. It may be worth concidering this feature of the breed though...I'd hate you end up with all of them getting hot and bothered in the nest boxes at the same time
Perhaps a selection of breeds would avoid you putting all your eggs in one basket....., Sorry, I just couldn't resist that one

Buffy