1. Some pretty buff orpington pullets close by and considering getting one or two of them. I've read that they are docile and can get harassed by chickens in a mixed flock. How often of an occurrence is this? Is it something that will work itself out generally or is there likely a severity to the 'bullying' that will lead to major injury?
There is a difference in what might possible occasionally sometimes happen and what will without a doubt absolutely happen each and every time. A piece of space junk might fall out of the sky and hit your house. You might have a fender-bender next time you go somewhere in a car. The sun might shine today where you are. Somebody somewhere on the earth will see sunshine today.
You are dealing with individual living animals so it’s impossible to predict exactly what any one individual will do. Each breed has tendencies but each individual has its own personality. And I find strain more important than breed. What I mean by strain is that if you selectively select which chickens on the flock are allowed to breed by specific personalities, you will eventually get a flock where most of the chickens in that flock have that personality. Hatcheries don’t generally select their breeding chickens based on personality. People breeding purely for show generally don’t. They are generally all breeding for different traits. It’s really rare to find someone who is really breeding for the personality the breed is supposed to have.
I’ve had a buff orp hen that was the dominant hen in a mixed breed flock. I’ve had a buff orp that was the lowest ranked hen. Same thing for Black Australorp and Speckled Sussex, sometimes high, sometimes low. Any individual might be top or might be bottom. If you want buff orps, I would not let a worry about them being picked on slow me down at all.
2. Introduction at night likely the best method? While they're roosting just slide the new chickens on the roost along side them? Or just put them in the coop and let them pick their place?
I wrote this for another thread but you might get something helpful out of it. The takeaways I hope you get from this is that the more room you have the better and that each of us have different conditions and situations. Personally I would never just throw strange chickens in the coop at night with others and hope they get along. Sometimes that works fine, but with that flock and those chickens about any method would work fine. It’s when the weaker chickens are getting unmercifully bet up that they need room to run away.
I’m going to give you a long answer because there is no short simple answer other than maybe. Hopefully some of this will help you make that transition easier. I don’t know the age difference in yours, but obviously it’s enough to cause problems. Even if they are the same age, you can have problems. Something else I’ll mention. Just because something can happen does not mean it will each and every time without fail. You are dealing with living animals. They don’t always act the same way.
One thing to look for is that it is possible for chickens to recognize which chickens belong in their flocks and which don’t. They might attack any strange chicken that does not belong to their flock. This doesn’t happen each and every time but it happens often enough to be a concern. A good way to help with this is to house the chickens side by side for a while where they can see each other but can’t attack each other. I suggest at least a week. By then they should recognize that each other have a right to be there.
Another thing is pecking order. They are social animals but to live together peacefully each chicken needs to know where it ranks in the flock. What generally happens when two chickens meet that haven’t worked this out is that one pecks or somehow tries to intimidate the other. If one runs away, it’s settled, though there may be a bit of chasing to drive the message home. If one does not run away, that’s a challenge and things can get violent. Usually one of them quickly realizes that they really should run away instead of fighting, so it gets settled. But sometimes they are evenly matched and it really gets violent. Death and destruction really doesn’t happen that often but there is one big key here. You have to have enough room for the loser to run away and get away. The tighter you have them packed in there the more dangerous this becomes. I don’t know how much space is enough space. That’s going to vary by each flock. Each flock has its own unique dynamics.
Another thing that will probably concern you. A more mature chicken will always outrank a less mature chicken and they can be pretty bad bullies about it. That’s probably some of what you saw. The more age difference the higher the risk. How they handle this is that the younger run away and very quickly learn to just stay out of the way of the older ones. They pretty much form a separate flock until they mature enough to force their way into the pecking order. Again the key is that they need enough room to run away and avoid.
A lot of us integrate chicks with the flock all the time and don’t lose any. Broody hens successfully do that all the time, often weaning their chicks and leaving them on their own with the flock at four weeks. I’m not a broody hen that takes a few weeks teaching the other hens to leave her chicks alone so I wait a few weeks longer, usually mixing them at 8 weeks. But I have a lot of space. If space is tight, it might be better to wait longer, maybe even until they are pretty much full grown. We all have different conditions.
There are some other things you can do that can help, other than providing as much space as you can. Unless yours free range all the time, put some things in the coop and/or run they can hide behind or under, some way to avoid the older ones or at least stay out of sight. And house them side by side for a while.
Provide feed and water in different areas. That way the young can eat and drink without challenging the older ones.
One of the places I see the worst brutality is on the roosts as they are settling in for the night. I suggest you provide extra roost space so they have room to get away, especially while some are too immature to force their way into the pecking order. I went so far as to provide a separate roost, lower than the main roosts and separated a little horizontally so they have a safe place to go that is not my nests.
As I said, many of us do this kind of stuff a lot. Sometimes it goes so smoothly you wonder what all the fuss and worry was about. Occasionally it gets pretty violent. Usually it is somewhere in between, with some pecking and chasing but no real harm done. I wish you luck with yours.
3. If the orpington isn't something that will work out; other breed suggestions that will 'fit in?' Leaning towards Naked Neck and Marans. No experience with either of them; preferably breeds that aren't generally flight.
It’s just pot luck how the individual chickens you get will interact. Since Easter Eggers are not a breed but are just mixed breed chickens that should have the blue egg gene, there is absolutely no telling what their personalities are to start with. Since they are not a breed, they don’t even have tendencies. I think Buff Orps would be as good a choice for you as any other, but if you are not comfortable with them, I suggest you go through Henderson’s Breed Chart and look for breeds that take confinement well and are not flighty. Not that you get any guarantees there but they do have “tendencies” and that’s the best you can do as far as I am concerned.
Henderson’s Breed Chart
http://www.ithaca.edu/staff/jhenderson/chooks/chooks.html
Good luck with it. Odds are you’ll be successful whichever way you go if you use just a little bit of planning.