One, yes in this case you would need to make a Bluff check to disguise your intent to grab someone, although that's only if you're actually using the Ready action to grab someone as soon as if you have an opportunity. If you're just standing there talking, and then decide "hey, I want to grapple that guy", that's probably still a bluff check to get a surprise round, but if you win initiative you also get to go first and grab them before they get a chance to move out of your reach.

Two, yes, but since it's a little awkward trying to grab someone through a narrow slot, even if you can fit your whole arm through it, he will have Cover (+4 to his CMD, which you need to beat with a grapple in order to grab a hold of him). On the plus side, since there's a door between you, he won't get an Attack of Opportunity to shiv you while you're making a grapple check, as the usual rules for making most Combat maneuvers like Grapple.