I think a rule of Thumb is about 90 days with no signs of distress.. I would think having 6 gecko's vet checked  may cost more then the gecko's themselvs . I quaranteen every animal I get  no matter  how good a breader it comes from ... I am interested in hearing more opinions  on this

I quarantine everything for 3 months, and I don't believe a vet check would be sufficient just because reptiles are soooo good at hiding illness, etc.

Ok so i should quarantine them. What should i do or be looking out for? I've never quarantined before which yes i know if a BIG risk but i want to start getting into really good habits.

For quarantine, I put any / all my animals on a white paper/paper towel substrate so mites are easily seen. 

For cresteds, it's actually best if you can quarantine them separately to monitor if each one is eating and pooping. But with six I know that might be hard to do. The next best thing is to weigh them periodically. You'll need to get a gram scale (I got mine at Walmart) - a food scale works. Make sure they aren't losing weight - this could be a sign of an internal parasite. Make sure they seem active (not lethargic). They may not move around much during the day, especially at first, but they should be moving around at night. If you are oh-so-lucky enough to catch a fresh "dropping" you can check it for worms. As long as their poop is clear of worms and formed (not runny), they are eating, they are active, and they are gaining weight for a solid stretch of time (3 months is what I do) then they should be good to go. Hope this helps! =)