On the black chicks, yes the barring gene should be the only thing affecting whether they have white dots on top of their heads (white dot male, no dot female.)
Yes, you should be able to sex the black ones. For the lighter ones, it MAY be possible to sex them too, if you can identify which differences are caused by the barring gene (vs. normal individual variation), but otherwise yes you could just treat them as normal straight run chicks, unsexable until they get a little older.
If you keep them to watch as they grow, I'd love to see updated pictures over time!