In my opinion, buying chicks from a hatchery or hatching the eggs yourself is best from a biosecurity viewpoint, but best does not mean the other way is bad. I may think that chocolate ice cream is better than strawberry, but both can be real good. Chicks from a source other than a hatchery should be treated as suspect. You really don't know how biosecure they are.
I think quarantine is a great tool when used right in the right circumstances. Used right means truly separating them. Some diseases are spread through the air, so you need to keep them far enough apart so the wind cannot transmit a disease from one to the other. You need to use different tools and containers when working with them. Don't carry food or water in the same container and use separate food storage containers so you don't cross contaminate. Wear different clothing or at least different shoes with the different flocks. You could go so far as to clean a wheelbarrow wheel before going from one area to the other. Not doing all this does not mean that the quarantine is totally ineffective, just that it is less effective than it could be. And based on your circumstances, you have to use common sense. Theory is great, but sometimes it is not totally practical. Just do the best you can.
Tbis section may sound like I'm arguing against quarantine. I'm not. But a few things to consider. Some flocks have diseases that they are immune to. They are infected and can infect other birds, but no matter how long you quarantine them, they will never show any symptoms. Coccidiosis is a great example. They may have it and can infect other birds, but they are immune! If a flock has been closed for a couple of months, they have effectively been in quarantine already. A closed flock means they have not come into contact with any possibly infected birds. One argument against this is that the stress of moving and quarantine may weaken their immune system enough for some symptoms to show. It depends on what the infection is. But in general, if the flock has been closed for a while, a quarantine won't do a lot if good.
If the birds have been exposed to other birds, then obviously a quarantine is a great idea. This exposure could be from new birds introduced to the flock or they may have been to shows or swaps. A lot of people do not quarantine under these circumstances and don't have problems. Just because a bird might be infected with a contagious disease does not mean it is infected. But when one is, the results can be catastrophic.
One more point. It is possible your turkey is infected with something but immune to it. Your turkey may infect the newcomers.
I'm not going to try to tell you what to do. My circumstances are different than yours. I only hatch eggs or get chicks from a hatchery because of biosecurity. I do take it seriously. But many people take it a lot less seriously and do OK. Quarantine is inconvenient and many of us don't have the facilities to do it right. Hopefully this helps you decide what is right for you. Good luck!!