I've only had a few hatchery Speckled Sussex hens, but I was less than thrilled by their egg laying. Medium-ish eggs, and more like 4-5 per week. The roosters are gorgeous to look at, but wouldn't be my first choice for egg laying.
As far as my comment about it not mattering what rooster you get, I guess i didn't make myself clear. I meant any of the higher production bred rooster breeds, they'll basically be interchaneable since you're doing mixed breeds. You will have a difference in carcass size, if that matters. Leghorns are little birds, and they make more little birds. Now, for the pullets, that can be a good thing cause you get layers that churn out the eggs and don't eat a crapton of food like say the big buff Orpingtons. But, for butchering cockerels, not so much.
With an order that big, were it me, I'd not add another male. I'd wait and see what I actually received from the hatchery. You may well get an Oops or two, of a breed you'll want to use for egg production breeding. And if you don't, well, for most of us, cockerels are very easy to come by. Other folks get Oops birds and would be thrilled to their toes to find a breeding home for their bird. You'd know genders by 6ish weeks, young enough you could easily add another cockerel at that point without causing huge issues with the social structure of your flock.