Concerning your first question:
The second approach gives one or two advantages. First you can see the relation between the item on the dropdown and the actual address. Another advantage is an interface that easier is understood: If additional information is visible, an item was selected.
What I generally dislike about the whole approach is the switching of interface element: Click on item, text information gets added BELOW. With this, the dropdowns will be forced to MOVE (especially on mobile devices, where relevant content will get pushed out of the screen), which generally is a bad thing, since the point of attention moves. The information is not lined up nicely, so users can digest it easily. So I think mixing up dropdowns AND a selected list is not the best approach.
What you could do is customize your dropdown:
With this you can get rid of changing the ui element, while still provide possible responsive behavior. Maybe you could try to see if this can still be a native dropdown field, since that would be important for mobile devices.
At the same time, information is lined up easier to read.
Concerning your 2nd question:
It does not matter if you go for 3 or 4 or 5 columns. Generally: The more information, the longer users need to understand. So if you can reduce it, reduce it. From a responsive point of view, the important thing is to create content boxes, that you can realign below and next to each other. So yes, your approach is a possibility.