Hi, Steve. Everything you describe can be done easily in the cart - by someone who knows what he/she is doing. That's not me. You cannot do what you are describing in the actual checkout however.
I have another idea for you: do this through shipping method. Add custom shipping rules like:
Picked Up at BWI Lounge
Picked Up at MCO Lounge
...
You could alter the checkout language setting that instructs the shopper, e.g.
"If you are purchasing from one of our locations, please indicate which one. If not, choose your shipping method."
Hope that is helpful.