Looks like Blue with silver leakage to me - I would guess he came from a mixed color pairing.
Both are looking like pullets at the moment.
How old? 1 and 2 are looking like cockerels, 3 is iffy, 4 and 5 look like pullets so far.
A straight up cross of Naked Neck and Silkie is a mixed breed. If you are referring to a Silkie who has the naked neck gene, that is a Showgirl.
Congrats on your new bird!
Are you sure just one Silkie is a good idea? They really do best with only other Silkies or similarly sized and tempered bantams, and it can be quite hard to integrate a single bird into a flock - especially a breed like a Silkie. In most cases it would be best to have two or three.
Silkies are constantly broody. They brood and brood and brood and once you think you've broken them, they brood again. Most of mine go 2-3 times a year if I actually let them hatch babies any of the times (rarely) and 4-5 if I don't. I don't even bother breaking mine at this point - they don't usually get babies just because I prefer artificial incubation, and they give up on their own... eventually.
Personally I would find the Polish-Silkie mixes far more interesting but if you want a neat bird who's also a decent layer the RSL 2 might be a good option.