I would be doubtful that you have undetectable ammonia in less than 7 days after you've added all those fish. It usually takes a week for the ammonia to spike, but who knows. Even if your ammonia eating bacteria have built up enough already to handle the new load, you are going to spike with Nitrites not to far in the future(1-3 weeks).
I've heard too many stories about LFS employees giving false readings to people. I personally will never trust them and will always test my own water.
NitrAtes would have to be very high to danger your fish, and in only a month, with most of the inhabitants being in there less than a full week, the nitrifying bacteria hasn't had enough time to build up their numbers to change the Ammonia & Nitrite into NitrAte.
As far as Stresscoat goes, it won't help anything here. It will not reduce the affects of Ammonia & Nitrite. It's like massaging someone's shoulders while they have a plastic bag around their face. Won't really calm them down or prevent what's really hurting them.
Try not to use any type of chemicals or medications or anything without first asking on the forums about them. A lot of them are at best useless and often will actually harm the fish more than help.
Ignore the LFS employees. I know there are some that know what they are talking about. About 1 in 50 probably. Not good odds. There are a lot of very knowledgeable people here. And if someone says something wrong, then 5 people jump them and a debate ensues until the truth is found.
Good luck and welcome to AC. Read around here a lot. Everything you need to know about keeping fish is here.