Here is a proposed layout using Atlas O45 and O54. It is very similar to the layout I now have using RealTrax O42 and O54, but I believe it is a little simpler. It still needs tweaking in a few places. The center is open, so nothing can be added there, but there is room for a yard in the O54 - O45 repeat. Only problem with that, it will take away room for accessories. I like it because it gives multiple options for reversing, and track to insulate to allow trains to pass. But, expensive to start over.
Criticize please!