The individual socket holders are locked in a track on the rack so they are always upright with respect to the rack. You can position the rack any way you want to.
Yes they will. Some people use the different color rails to make it easy to identify American and metric sockets in the toolbox.
Pretty sure they're plastic with a steel ball in the squares. I actually went out to look. Durable enough for me but I like them a lot more than the ones with a piece of spring steel in them and a plastic handle on them as these fit the toolbox well.