We need to expand beyond Earth
No we don't. There's nothing but a cold hard vacuum out there, with a couple of extremely inhospitable cold rocks.
There is almost limited energy. once fossil fuels run out, we will be left with essentially the energy that hits us coming from the sun (plus fission and fusion but... *waves hand*). There is a lot more of that out is space and we will probably want to tap into it. My bet is that eventually, the energy infrastructure in space will grow to the point that we'll both develop manufacturing in space and have people in space as that will be the least work intensive method to get that energy. From there, the infrastructure to support those people will grow until space itself can support itself. From there, we'll move out through the solar system and possibly the nearby systems harvesting materials as we go.