Do you believe that the universe is eternal?

We know that from nothing, nothing comes. So, if there were ever a time when there was absolutely nothing in existence, then nothing would have ever come into existence. But things do exist. Therefore, since there could never have been absolutely nothing, something had to have always been in existence. That ever-existing being is what we call GOD ,GOD is the un-caused Being that caused everything else to come into existence. God is the uncreated Creator who created the universe and everything in it.

No! It will be replaced by God's new city called the New Jerusalem as mentioned in Revelation 21.

Revelation 21:1

And I (John) saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea.

No.
It seems likely - based on current theory - that the still-expanding Universe will one day reach a point in its expansion - in a real sense, space will be stretched so thin - where it can no longer sustain its own existence. At that point the entire Universe will sort of "dissolve". It will take several billions of years for that dissolving to occur (it will occur at the speed of light, and start from the "furthest edges" and work its way inward)...

But of course that theory MIGHT be incorrect and the Universe MIGHT last forever. We don't know enough to be sure.

Define "eternal" so that it is relevant to an 11 dimensional object.

No.

Yes. It is constantly spiraling in perpetual motion, and the energy in the perpetual motion is what keeps it going. Once it stops moving is when it is done, so work to keep it going!