All of this is great information and it really helps!
I'm just nervous 'cause I grew up all my life on the West Coast, and lived a good while in the South. It's easy to figure out what to do and say in both those places, but this East Coast has me stumped. I worked as a cashier and was chewed out for saying "ma'am" to one lady, but then other people will say it's rude not to use "yes ma'am and no ma'am"
It might help if you consider the East Coast as three separate regions of the US, not just one. It's my impression that the three West Coast states have more in common than the 15 East Coast states do. Not that the cultures of the three states are identical, but that they share more common factors than the East Coast states do, on the whole.
There's New England: (Maine, Vermont (which I'm counting even though it has no coast line), New Hampshire, Massachusetts, Rhode Island and Connecticut. Then there are the Middle Atlantic States: Delaware, Maryland, New Jersey, Pennsylvania, Washington D.C.,and New York. And the Southern Atlantic states: Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, and West Virginia. (Although some put Virginia and West Virginia in the Mid-Atlantic--I could not find a consensus on this).
Each region has its own culture, shaped by the people who settled there, the terrain, history, economics, etc. We've even had a war over the differences between the states. So, yes, saying "ma'am" will get you kudos in some areas and dirty looks in others.