Congrats on getting the restrictions removed.:y: Personally I have never encountered a store with a metal detector but I'd say if they don't have a sign posted restricting guns then all you would have to do is show them your permit. I carry in stores that don't have signs but have yet to come across a store that has one. So if I saw a store with a sign like that, I wouldn't give them my business anyway. I carry everywhere unless prohibited by Law. Such as schools and government buildings to name a couple. But you have to be careful if you travel within the state because some city's have stricter laws include, Albany, Buffalo and Rochester. Don't take your gun if your going into New York City. You need permission from the chief of police in order to carry there and if you ask, you'll need a very good reason why.
I'm sorry I can't be more helpful but New Yorks gun laws are so messed up the best thing you can do is spend a day on the computer searching the internet then write down any questions you have and ask a lawyer. Luckily the county I live in and the counties am surround by are fairly pro-gun. So I carry all the time but I do sometimes have to enter a local government building for which I don't carry.