Destruction Help

[Xestro]

Hi
I have a few thing i am currently having a problem with.

First where can i find the things that are in the skybox in ep2s first mission?(citadel peices, destroyed city, etc)
Second where can i find the citidel destruction animation like this one here?

And the last question is a little more complex. Im going to have a barn, under the barn is a strider in the crouch position, when you get near it it will stand up destroying most of the floor of the barn. then it will try walking towards you and step on a propane tank(there will be a bunch) which will destroy the barn and kill the strider.
My question is how can i make this all happen and look good without tons of lag?

Thanks