Reply to "What size wire?"

I am using the conventional method with Lionel tubular track with American Flyer 3 rail switches. The switches have the option of regular operation or two train operation. My layout size is 6x12. Main part of layout has two separate ovals each with a passing siding. The inner oval also has one small spur. Have a small second level with a 3x6 oval. Hope that helps. I have 2 KW transformers. Planning on using one transformer for the two larger ovals with passing sidings and the other KW for upper loop and accessories and lights. Hope this helps. Thanks