I thought I was the only one that had a split run, I have a split coop as well. Simply because I couldn't get my bantams and standards to get along when I 1st got them, but I now have it opened up and they all get along (different flock members thanks to mr fox, but includes 4 roosters thanks to straight runs).
Anyhow, I wanted to add that given enough room and enough food and water dishes bantams and standards can be put together. you'd be amazed at the boldness of my bantam cochin hen, she stood up to my standard brahmas like they were nothing! She is less than 1/4 their size.
Do quarantine for a month, it can take longer than 2 weeks to see signs of cough/sneeze, and can give you time to get to know them.
If you cannot split your runs some people will introduce small numbers of birds using a large dog crate in the coop. Then they can see eachother without hurting eachother. I have had good luck introducing new chickens when done in large numbers, after quarantine, they are a flock and stick together when they meet the rest of the flock. Seems to keep the "old flock" busy when they can't decide who to pick on 1st.
all this will depend on your current hens, they may be very accepting of newcomers and it may be very smooth. The younger ones seem to get picked on more than more mature pullets. It is amazing to me that there is such a difference between a 3-4 month old pullet and a 5-6 month old pullet. They are much more self confidant the older they get. There will always be 1 hen that has to prove her place at the top, but I have never had any get even a spot of blood. Roosters on the other hand.....
good luck, I'm sure all will be fine!