People successfully add to their flocks all the time. Sometimes there are problems as I'm sure you know from this site, but this link discusses both quarantine and integration. I think it wil help improve your odds of success.
Buff Hooligans Adding to your flock
https://www.backyardchickens.com/web/viewblog.php?id=2593-adding-to-your-flock
I think a whole lot of whether you have problems or not depends on how much room you have. The more the better.
Another thing is for you to understand that they will work out a pecking order. They are social animals. They cannot function as a flock until they work out the pecking order. The trick is for you to know when it is normal pecking order stuff and when you should intervene. I think the general guideline of leave them alone unless you see blood is fairly good but it may not cover all situations. You just have to use your judgment.
A lot will also depend on your roosters. A good rooster will accept a new hen into his flock by mating with her, whether she wants him to or not. That way he establishes his dominance but also extends his protection to her. With a good rooster, that protection will extend to breaking up fights between hens if it gets too vicious. Not all roosters are good and some see new hens as threats to their flock instead of welcome additions. They are all individuals.
As I said, people are successful all the time. On here, you usually see the problem times and not the succesful integrations. So don't be afraid to try, but be aware of the potential problems.
Good luck!