Ok, so for some basics of quarantine, or at least on caring for a quarantined bird, you want no contact from the bird in quarantine to the birds who are not. You should take care of your flock first, then take care of the rooster. That way you're not introducing anything he has to your hens (but are introducing everything from your hens to him, good and bad). Technically, if you've stepped anywhere he has been or any part of you have been in contact with him, your shoes and anything else that came in contact should be washed. This is for the extreme case. If it's a concern, then putting plastic bags over your shoes that you can remove or have separate pairs of shoes to take care of him should be fine. The biggest thing is he has no contact with them, and that's even through his poop (which is something you should be checking on for worms or anything that doesn't look normal. Depending on his diet, you might want to wait a few days in case he's eaten anything that he wasn't supposed to). Some do say to keep a bird in quarantine so many feet from the flock. I don't know how far that is, though I want to say it's 30 feet? Personally again, I think contact is the biggest concern, but good practice would be distance as well, because the wind does blow.
In quarantine, the simplest answer is for anything that isn't normal. The biggest thing to do first is to check him over (particularly in his warmer areas) for mites. I highly recommend doing more than one check as mites can easily be missed. Next is to be watching his poop. I'd give him a few days to ensure he hadn't eaten anything that'd make it look different. Now, on this, I'm not an expert because it grosses me out. I do know it can be a way of finding things wrong, plus should be checked for worms. If you find anything wrong, it might be best to start another thread calling for the poop experts.
Then over the course of two weeks (or 30 days, depending how serious of a quarantine you're doing), you want to be watching his behaviors. Does he seem lethargic? Is he crowing a lot and making other normal chicken sounds, or is he remaining quiet like something might not be right? Check his weight if you can. Does he gain or lose weight, or stay the same? (If he loses weight, something's wrong. If he gains it, it could be he's still growing, but it also could mean he was poorly fed.) Then keep an eye out for anything else that might seem off. When you're not familiar with the kind of bird you have in quarantine, it's ok to question everything. Some things can be normal, but sometimes, like in the case I shared earlier, it can be the little thing that's off that could be pointing to a disease.
All in all, and maybe this is because I'm a little too trusting in this case, I don't think there's anything to worry about with this rooster and he'll probably be an easy first quarantine. Please don't get too stressed over him. I really think he'll be an easy case. And who knows? He might become the best thing that ever happened to your flock. He's a handsome boy and I hope this works out for you.
(And please don't be scared off my recommendations. I gave you some of the extremes in basic quarantine so you have them and can decide how far you want to go. My biggest thing is take care of hens first, then him, and wash hands after handling him. On watching him, watch for anything that seems a miss. Again, I think he'll be an easy case.)
