Lots of possibilties with all of that space! Some people create two scenes on a 4X8 layout like this by putting a divider down the middle, sometimes diagnonally to maximize the space. That way you could have two very different types of scenary since the divider comopletely separates the scenes. What railroad are you modeling? That would help determine some scenary choices base on the the parts of the country your line is located in. Do you have personal preferences for rolling farm land, mountains, desert, etc? Want a stream and a bridge? Again, lots of possibilties with your space!
Ralph