I have RIR, Plymouth barred rocks, and Australorps and they are all great layers, very intelligent and perfect for free ranging. PBR are actually at the bottom of my hens pecking order smaller of a bird, but they lay a lot for their size.
What I did for my chicks to introduce them to my older flock (hens ranging from 4-10years old) was put the babies in the barn coop. All my birds free range there are no doors closing them in and they come and go as they please. I kept my chicks in the house until they were about 5 or 6 weeks old. The weather greatly varies where I live. My coop for the barn is only used for babies and young birds. I put the babies in the coop (giant rectangle made of wood and chicken wire all around including wire floor with a wooden lid to keep predators out) during the day hours and brought them in to the house at night at first. I did this for 3 days and they started to get real fussy with each other so that was them telling me they were ready to stay outside and were getting bored and too cramped. I had a lamp out there for colder nights, but they did great. You want to make sure your young birds are at least half the size of your older birds or they will pick on them and can kill them if they are smaller. I left my babies in the barn box for about 1.5 months because the hens were so small (while my chick rooster was ridiculously larger). All the chickens saw each other and sometimes my young roo and an old hen would fight with the chicken wire keeping them safe. The old hens would go up the wire and watch the babies for 10-20 minutes. Eventually they all calmed down and no one cared about anyone. I then would let the young birds out during the day to let them get used to the barn and surroundings and so they could learn to be birds. I would advise first letting the young out with the old when the old birds are distracted by eating and good treats. Make sure there is enough so they don't fight. There was not 1 quarrel between the old and young. At night I would go back down and put the young birds back in the barn coop so they would be safe because they did not roost right away. I live in an area with coyotes, fox, raccoon, and all other things that are up late looking for a chicken tender dinner. My young birds (I have 3) now all roost 35' up in the barn rafters 1 hour before dark. I have no worries. They are all Australorps and they to me are one of the most intelligent breeds I have had.
About free ranging... This is in my years experience with chickens and I just am trying to put you at ease with some good points and worries you brought up.
I don't know if you have any roosters or can have any- I have 2, but I rarely have a hen go missing. Its usually the rooster who passes doing his duty to keep the ladies safe. I will sit out with them on a nice summer or fall day, but mostly my birds are alone for the day with the protection of the roosters. Also I doubt your chickens will hop a fence. Mine have never run away. I feed them good food/treats and the barn is "home" why would they leave.. The barn is the safe zone and they all make there way back to it well before dark. I highly doubt also they going to wonder far until they get used to what is all around them. I don't have a fence up around the entire property (only in the front with the driveway and it is a small 24" chicken wire fence) and they so not go over it. They will stick to shaded areas or tree lines to avoid hawks and will also stay mostly grouped together. I do have 1 or 2 hens that are obviously independent gals and once in a while will go off either with each other or alone without the group or roosters.
The more you let them out the quicker they will learn also. They have the instinct to know they WILL get eaten if they don't roost, come in before dark, stick to the tree line, etc. I worried about some of these things too at first. Some summer days I have no idea on the property where they exactly are.. then I go around a corner and they are peacefully and quietly pecking at the bugs and the ground. Also a cool thing you can teach your birds is to come when called. My birds hear me whistle a certain tune and if they are in hearing range they come running all at once. If you can't whistle yourself some people use a whistle or other noise. Its helpful when they are in tall grass or under a tree and you cant see them and just want to know about where they are before you go to work.
Also if you don't have a rooster, you can take your dog out by the barn to potty while your birds free range. This will keep away most predators that find their way to your barn. I have 3 dogs and do this with my dogs. My dogs (even though all hunting dogs) do not go after my birds though so you may want leash your dog since you think she may be aggressive with your birds. Your birds will be SO much happier when free ranging and you should also notice that your egg yolks will get darker like a burnt orange. My hens lay very dark yolks and its from free ranging. I also have almost no spiders, ticks, etc near my house from the birds ranging. They eat cracked corn, fruits, veggies, when they are around the barn, but mostly they free range. Also I noted that because my birds free range and I have other animals to tend to in the AM... that my chickens will all leave in the AM to find breakfast before I am in the barn. They know I will be in the barn about a certain time will go back to the barn to wait for me and their treats/breakfast from me. Then they will go back out to free range.
Hope something in this helped! Good Luck
