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These are all fantastic answers. For number 1 I'd also add "and also depends on what the thief did to trip the ogre, and how we narrated it falling" to it, but that's pretty much it.
Also, #4 is just plain fantastic. Can I play at your table, Threlicus?
I think all in all, the thrust of what is being said is if you want mechanical bonuses, aid; If you want better fictional options, do something fantastic, and probably have someone else aid too ;)
Edit: not that aid shouldn't change the fictional position, too, just that for clear mechanical bonus this is where you turn.
As far as number 5, hack and slash or defy danger work well. I might even call it a sneak attack if the thief had positioned himself that the move was coming out of nowhere. All good solutions, depending on what exactly is said.