I was going to say the same as HesterF.
The whole point of the sex linked thing is that you could then dispatch the cockerels as day olds and didn't have to feed them for several weeks till you could distinguish them.
Given that your project is presumably to get a good price for your pullets and have something worth putting in the freezer, you will only be producing crossbred pullets with nothing special to commend them, and nice tasting cockerels for your freezer that you could have puchased cheap from someone else who just wanted rid of their own young males.
Just a suggestion - why not choose a heavy breed that really appeals to you - like for example Faverolles. There's plenty of others but I'm just giving them as an example as they were specially bred originally for the Paris meat market. You can get £15 upwards (easily) for your pullets as they are a rare breed, reasonable egg layers, and will breed true; but you'd struggle to get that for your cross breeds, which won't breed true and therefore have no unique breeding value to the purchaser. In addition you'll produce table birds worth eating.