There are no correct absolute answers in your position. Chickens are living animals and almost anything can happen. We can tell you from our experiences what we think will happen or what happened to us, but there is no guarantee that you will have the same experience.
First, quarantine. If your friend has not introduced any new chickens for the last couple of months, I don't see a big benefit in putting the rooster in quarantine by himself. If he has not been exposed to any new chickens lately, he probably has a immumity to any disease that he has that he could give to your girls. He will probably not show any symptoms in a month quarantine by himself. To get a meaningful quarantine, you would need to house one of your girls with him to see if they give each other any disease. It is just as likely that your girls have a disease they have developed an immunity to as it is that he has one that will affect them. This way, you put one of your girls at risk, not all ten. Parasites like mites, lice and worms are different. It is not a bad idea to check him carefully for any of these before you mix them.
It is really hard to say what will happen in these circumstances. It depends a lot on the personalities of the individuals and the maturity of the rooster. One really complicating factor is that a mature hen will sometimes totally reject an immature rooster. If he cannot sway her by the pure brilliance of his maturity and personality, more mature hens will often beat up a rooster, making his life miserable until he matures. I had a 15 week old rooster that the year old hens accepted no problem. I've had older roosters that they would not accept. Age is a very important factor, but it is not the only one.
An immature rooster often has hormones out of control. His instincts tell him that he absolutely has to make sure that every egg laid is fertile. It does not matter if the pullet or hen agrees, he has to make sure they are fertile. He is often bigger and stronger and can force his way, but sometimes the pullets or hens vigorously resist. This is especially true of pullets that are not yet laying. It is not just the rooster and his brilliant personality, but also the maturity of the pullet. For the act to go smoothly, both the rooster and the pullet have to do their part, otherwise it can get ugly. Flocks made up of adolescent roosters and adolescent pullets often are a lot more exciting than flocks with mature roosters and hens.
When you have a flock of just hens, one will often take on the roll of the rooster in flock protection, finding food, all that. If you introduce a rooster, she may fight to defend her dominant position. But sometimes she seems to be the first one to welcome the new rooster and stick by his side.
Even with the ages of yours it is possible that you can introduce a rooster and things will go very smoothly. I think it is more likely that things will get pretty exciting for a while, until they mature some more. It may take a month or it may take several months for them to settle down, if they have initial problems.
When introducing a rooster to a flock of hens, I suggest just turning him lose with them. I don't see a lot of benefit in housing him next to then for a week or so, where they can get used to each other like I would suggest in a normal integration. A good mature rooster will immediately mate with the hens to establish his dominance and they will accept him without too much fuss. That's when it goes great. Or they will resist his advances whether they are used to him or not. When you are ready for them to mix, after quarantine if you decide to quarantine, just let him go where the hens have room to get away if they want to and see what happens.
Good luck! I don't know if this helps you or not.
girls are great at laying.
