Also working on 12x6 layout....have been through several designs and still not settled on one...I am going to use Atlas O track....you can use up to O63 minimum curves without a problem...I plan on using O54 to leave some room on the sides for scenery and/or sidings...I am also looking to operate rather then just running my trains...so there will be an inner loop of O54 with 3-4 sidings...within that I want a small town on one end and mountain scene on the other....a 4x3 section can be added later on for a switching yard/roundhouse...I like to run freight more then passenger trains but will incorporate both....I also use SCARM for layout planning....very simple to use and great tutorials on you tube....my benchwork is plywood top with homasote on top of the plywood....on top of that I am testing 2" extruded foam which will allow me to add depth without adding any grades in my first stage....once things are in place I will think about a 2nd level.....will be following your post to see how things move along for you....good luck and enjoy....
