With 8' wide tables, you will have to have walking access on all sides (though you may already know that, just can't tell from picture and diagram). Also, be sure to leave plenty of room to access any other home infrastructure (plumbing, electric, etc.) that might be anywhere near your layout. Finally, incorporating 4 different levels sounds like fun, but watch your grades (<4% is preferred), watch your grade transitions (at start and end of each grade), and watch how this may affect the scenery and size of curves you are thinking about.
Chuck
