I've been looking at getting into map design

But I don't know the limitations of Hammer and the Source Engine.
Can someone who knows a lot of technical details tell me which of the following are possible?

• Structures that move relative to the map, but can be given a spawn room and have engineer build on them
• Have submarines that move about (Water outside, air inside)
• Use the linked_portal_door entity from Portal 2 in TF2 (If the two things listed above are impossible by normal means, moving portals could perhaps be linked to a stationary submarine)
• Convert 3D models into world brushes
• Have a procedurally-generated ghostly train track appear with the track going underneath every sniper in the map

I've been looking at getting into map design