I'd prefer no.1, John.
If it's going to be 4feet wide,I imagine you'll be able to stretch it quite a lot.
Is it to be permanently-installed somewhere, or is it to be "portable"? It's going to be shockingly heavy if you build it as bomb proof as you have in mind!
Here is a nice simple one that was an exhibit at the 2012 Slot Far Festival here in UK.
This looks as though it's 8x4; entertaining enough by itself, but stretched to 16ft, might take 3-lanes.
David.
ps: 3's nice. Would the straight be elevated slightly?
If all the curves were at the front, you could make the baseboard "dog-bone" shaped, which would cut down on the leaning over for marshalling.