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As noted by Lei, the answers to your first two questions is normally yes.
In answer to your third question, it depends on what you're trying to do and the capabilities of the platform. If you want to configured explicit QoS per logical interface, devices that allow that may "balk" at also assigning explicit QoS at the physical interface. Also explicit QoS on the physical interface might be limited by what it "sees". For example, physical interfaces, usually by default, will see a tunnel's outer packet as just the encapsulated packet while QoS on a tunnel "sees" the unencapsulated packet.
