Both lay but not like chickens that are breed as prolific layers. Silkies are the best broodies hands down. A silkiie will set on any other chickens eggs,hatch them out and mother them.
IM getting the silkies mainly as pets and will use them to hatch some eggs now and then.
As for introducing chickens of different ages. You need your chicks to get close to the same size and then add them to the flock gradually. I have my hens in their house and have moved the 4 chicks (7 weeks old out to the house in a seperated temporary area where they can all see one another but the young ones won't get picked on. After another month I will have them all together in the run during the day but sleep seperate until they are close to the same size. I will then put them together and there will be a bit of sqaubling but they will develop a natural pecking order on there own.
I will add another group to the flock later this summer as they will hatch around April 21st or so and I will be getting the chicks I ordered from Mintana Mills about the same time so all the chicks will be together and I will grafually intergrate them with the flock in June or so.
My friend here in Billings want a few silkies and showgirls as well so it all depends on how many hatch. If your interested let me know and i will PM you after the hatch.
Hope you can get yours locally as that makes it much easier. I would order 3 extras as sometimes you will lose a couple chicks. If your just wanting hens you will need to tell the store that, as alot of times they will only order a straight run.