I use a wire dog brush to fluff, not to get out mats. If you did a good job of washing, the feathers should be clean and straight. The only reason you'd see clumping of feathers is if you didn't fluff well enough during the blow dry. If you actually have feathers stuck together-- like under the rear area, those will have to be carefully pulled and worked apart. You can't run the brush through their feathers like you do with fur or hair.
It's not very accurate, but by 3 months, I look at their combs and determine who is getting a wider comb path and comb growth. By that time, there should be zero comb growth on a female. If there is any growth or bump there, it's usually a boy. Of course... you could still have boys that spring up later and are slow growing. For example, I have a gut feeling that two of my chicks are boys and their comb path has not widened or grown yet. No comb growth at all. However, by the look of their beak and the crest coming in, I'm pretty sure they are boys. You can have some very slow maturing boys. So just because you have no comb growth doesn't mean they aren't boys. I'm actually really, really hoping mine are boys, so I'm crossing my fingers on these guys. If you have hatchery birds-- I don't know what to tell you. They don't develop the same, and even females will get pretty large combs. But the nicer quality birds can be the most difficult to determine. It doesn't matter to me if I have boys or girls, so the stress of worrying about it is not a factor and I can be more neutral in my opinion and not jaded by the hope of having a girl when I'm looking at them.
