The biggest issue with Lavender Orpingtons is the feather shredding gene that makes their feathers look ratty and messy.
You can't see signs of it until they start growing their feathers.
Is it possible you can hold off selling any for a while?
26 is a good number to choose a handful from, but if you sell soon you miss out on the benefits to be choosy.
As for other traits, body mass is important in Orpingtons. If you look at the chicks from above and a bit behind, some will look more square and fat than others. Some will also have bigger feet.
Both of those qualities could weight the selection towards males, so keep an eye on other gender markers.
You also want to look for floof. It shows when they are feathered.
I think I've seen some little chicks display more down floof than others when compared closely, but it's hard to be certain what they will turn out like.
Look at the underskirt (around the upper thighs and navel) for chicks that have more pouf than others.