There aren't any rules. Since you're ok waiting til you get to Europe, personally I'd stop worrying and tell yourself you're going to
enjoy a spot of luxury shopping in the US. Be nice, be yourself. Drop into ALL these three boutiques
with the expectation of a fun browse and IF there's anything you are interested in, ask to see it. If there is not, ask if they happen to have any Picotins.
There is a bit of a bag shortage at the moment, and most SAs (not just leather) in big stores like BH and Madison have a limited number of things they can offer each day. But walk-in offers still happen all the time.
Don't burn out either your wallet on things you don't want, or your psyche on it being a game. You can always get your bag at resale.
If you want, stop at
Fashionphile/Rebag/
TheRealReal first to educate yourself on the bag and possible colors.
This is supposed to be fun, and it can be.