Howdy!
Hi Scott.
God! 4'x8' for N gauge is an empire! Giant in layout terms. You may find it easyer to build it in modules 2'x4', this might be easyer to compleat.
If you want to build your layout 4'x8' then you realy need to plan out what you want your train to do. IE run from town to town, go from the sea docks to the interiour factories, conect a big city with small towns or suburbs. Then you need to decide what your track elevations will be keeping in mind the grade you want your train to clime. Most guys run between 2% and 3.5% grade. A 2% grade means the track rises 2" in 100"of track length.
These are all personal choices and it would be hard to design a satisfactory layout without realy knowing what you want. Mabie if you look at some layout pages one might find one that clicks for you, but to custom design one requires some more input, if you want to be happy with the results.
I think you will find that planning, planning, planning should be the order of the day right now. You could always set up your trains on a bare piece of plywood just to get them running and see what posabilities you come up with.
As you said in your post "something interesting" is in the eye of the beholder. Surf more posts and see what the other guys are doing. This will give you a better idea of what that "something interesting" might be.
Just tryin' to help
TrainClown
PS....The more planning you do now, the less rebuilding you will do later.