I agree, they are broody little buggers. Won't find many other breeds that compare, other than cochins and a few others(and they still aren't always quite as good, though there are some great broody cochins)
I wouldn't crossbreed silkies. If you want white birds, buy white birds from a trustworthy breeder(white only being an example color, get whatever color you want lol). I have bought birds that looked purebred in the past, only to find out they weren't(they gave me the weirdest combinations of colors and feather textures lol.
Unlike some other breeds, maturity is a crapshoot with silkies. It all depends on their genetics, what lines they come from, how purebred they are, etc. I find that my silkies from cacklehatchery(absolutely will never be show birds if I may add) mature faster than my good showbirds, though that might just be my luck. But I agree with the 6 months to 9 months until maturation(with random birds that might mature much earlier and much later) (and again it depends on the birds' genetics)
Silkies are never good layers, mostly due to the fact that they are almost always broody. But you can use this to your advantage by letting them hatch out other breeds of poultry. I love my silkies dearly, they are so sweet and docile. Hopefully mine will start laying soon, as they are around 7 months old.
But again, unless you don't care what your birds look like and don't really care about exhibition and selling purebred babies, don't cross different colored silkies(excluding splash, blue, and black)