I agree, sometimes you recognize a rooster chick, practically right out of the nest, other times, it is not so clear. The bottom center one, has that rusty coloring, and I think the beginning of the hackles?
And the other two, their tail feathers have a suspicious curve to them to me.
Hope the...
I could be wrong, but I see three that I am suspicious of. The second bird in the top row, the second bird in the middle row, and the 2nd bird in the third row.
I would not add a rooster until most are laying.
I think I would hold off on getting him til you know for sure.
Mrs K