Well my new layout will be in a 20x20 mostly square shape and I'm limiting it to 4 feet in width so I can reach everything on both sides. I will have 2 mainlines with 1 being elevated (but connected). I will have a third, branch line which services a small town, yard and industries and connects to one of the mains but only runs over 3 of the 4 sides of the layout. While 20x20 seems like a large space it's really not when you start adding things and want to keep mainline curves at O72 (or larger). I agree with what Melgar and Richie posted and personally feel you can easily go overboard on track. In the end it all comes down to what YOU want and prefer so do what makes you happy. Besides, it will give us something to give you grief over at breakfast in York. 
-Greg
