I see some people have recommended white leghorns.
I raise white leghorns to sale eggs and chicks. I can tell you they are great layers 6 or 7 eggs per hen summer and winter. They are very hardy birds. The one thing you will need to do for them make sure they get sprouts or leafy vegetables...
My main coop is 4'x4'x8' placed inside a 7'x14' run 7' high.
We have 14 hens and a roster in this one. (I could put up to 25 hens in there) It has 8 nesting boxes and a dirt floor. I put a 3' door on it . It make's easy to clean out and get the eggs.
Very cheap to build. Also check...
x2 on mtngirl35's post.
If you go to fast you will stress out your flock. The new chickens are seen as invaders and not new members of the flock. And you may even end up with dead birds and no egg production .
Then I would just watch them see how they act in the morning. It is only going to get colder. And you don't want them depending on the heat lamp.
Chickens are much tougher then people give them credit for.
Good luck
If you go through the right steps you should be fine.
Try this link for help http://www.fresh-eggs-daily.com/2012/04/adding-to-established-flock-pullet.html
Good luck
I sell eggs and chicks from home. We also free range our flocks.
I 30 laying hens 6 roosters. I cannot have hen or a rooster running around that I don't trust.
And I don't have that much time to spend on one bird.
As I posted in this tread before we have a roo in our axe pen for this very reason.
I prefer to hand raise my roosters because it is easyer to teach my little girl to work around them and they are used to her.
But yes if they go bad we love bar-be-que chicken.
There is a couple of ways to deal with this;
1.Put blinders on the roo
2.Get a chick and hand raise it.
Behavior training takes time a dose not always work.
We have RIR roo in what we call the axe pen for this very reason. A rooster can jump high enough to hit a child in the face and he may not stop once she go's down.