Just a quick question. So in return to echo base there are the tunnels which basically means there is a opening in the wall. Now it is only 1 space, does that mean the Wampa's need to turn side ways to go through the tunnel? What about a Nexu that is 4 spaces that does that mean that he can't fit through the tunnel?

Yes, no figure can move through walls or doors, but Wampas and other 1x2 figures can move through if they move sideways or rotate through.

Nexu cannot move through, but Nexu can Pounce through - Pounce is a placement, not move.