Not sure about the console commands for single player. I was going to look into that myself to set a few warp points in my current map (keep getting killed).
Obsidian can only be made from stationary lava - not flowing lava. So your idea wouldn't work.
If you really need to know where resources are on your map, there is small program called Minutor (located here
). The slider at the top cuts through each level in the map and you can quickly locate the closest diamond or iron. Can also be used to find the mob spawners if you are looking closely. (square shapes in the display).
Yes, obsidian can be mined with a diamond pick.
I've also tried to take the mob spawners (cages) with me but they can't be taken. I now construct a water trap just outside the room to kill the mobs. If you want to stop them spawning surround the cage with four torches.
From what I understand, spawning a cage from an admin command only will spawn pigs.
Hope this helps.