I have silver spangled Hamburgs; ordered from McMurray. I was able to sex them at a week old; the male had a very prominent comb already by then.
Answering your 2nd question.. Most likely, mine are evasion pros, very flighty and the rooster is not one to mess with; he's small but very protective
I crossed some with my blue Andalusian, and here are 2 of the resulting blue chicks:
They're only a week old, but so far no sexing can be done because they lost their fast feathering trait in the cross, and the one that looks similar to yours got the single comb in the cross too, so I can't quite tell sex yet, but blue they are
Good birds, they eat very little and stay pretty much hidden all day; I'm actually frustrated at them right now, as they sneak into the duck nest and lay there instead of the coop, so finding eggs may be an issue, just FYI