Plymouth rock chickens question

[JULIE L CORWIN]

I have several barred Plymouth barred rock chickens. That are a week old.
My 2 questions are
If I get another batch from the hatchery and add them to the current bunch. They would be only a week apart in age. I know that there is a pecking order.For top chicken. If they are only a week apart. Would they get along?
Second question
Out of the next group. I am thinking of adding a White Plymouth Rock or two. I have only read it on this site. hubpages.com about the White -Plymouth-Rock chicken. It says you will notice that the chicken will start growing a downy like undercoat of feathers. This is in preparation for winter. These feathers are close to the body skin and will help keep the chicken warm. If you heat your coop. They don't grow these.That they will sucome to colder weather. So you should not heat your coop.
Do the Barred Plymouth Rocks also grow these feathers? Has anyone heard of this? I only found it this one time doing research.

 

[SueT]

Some people have successfully integrated chicks that close in age. You could make a temporary divider just in case, let them see each other. You will probably want an extra feeding station for the newbies.
All chickens have down to keep warm. You do not need heat for older chickens. Using heat in the brooder for babies is necessary for 3 weeks or so. They will grow feathers faster if you wean them off heat faster than the normal recommended 5º less per week.