I need advice!

[sourland]

What exactly is the quarantine for? I would figure diseases but if it’s just in a wire cage won’t they get infected?

I was all prepared to comment, but @Ol Grey Mare stated how things should be done. That is a beautiful rooster. I'd be tempted to build him his own coop and get some little hens for him.

 

[Ol Grey Mare]

A proper quarantine is at least 30 days. It is "passed" if the bird remains completely healthy for that period....the idea being a bird may not yet be symptomatic at the time of purchase, but could be carrying illness.. quarantine allows time for symptoms to develop without having exposed your flock. There are also some illnesses for which a bird can be a "Carrier" for the rest of their lives after having been exposed and survived initial illness. The process of moving a bird can be a stressor and stress is often what can bring out symptoms of that" sleeping" disease. By having the bird separate from your main flock during this time of stress to see if it does bring about a period of being symptomatic you avoid having infected your entire flock needlessly. Quarantine is not a guarantee that the bird is completely healthy or that it will not expose your flock to something, but it does greatly reduce the chance of that

 

[ChickNanny13]

He is cute, no wonder you want to keep him

 

[rkapfen]

He is cute, no wonder you want to keep him

And he’s so gentle! He’s letting us hold him and pet him just fine. Which is great but makes me worried that my more dominant larger hens (Brahma, Cochin) are going to attack him

 

[Ginmary]

He's definitely a bantam breed with the size of his comb and wattles. I am trying so hard to get my Seramas and my larger hens to co-exist. They are in a large dog kennel (8'x4') in the center of a room where the 3 large hens are. When I let them out together, the 2 female Seramas are getting better and don't mind the big girls but my Serama roo is still going after them. In spite of his size, the big Buff Orpington and the Americauna run for their lives when he starts to go for them. It's rather comical, they could probably squish him if they stepped on him.
It's all in the attitude! So, your roo could be more of a problem to the hens than they are to him. The proper integration will hopefully work things out.