Greg,
Your plan picture is missing some key "reach" details (dimensions), so my main comment is that any engine that derails on a roundhouse lead track near the turntable looks like it will require a long reach over track and scenery to fix the problem. Big, heavy engines will make that reach just a bit harder.
And, here's a "something to think about" comment. Looks like you have quite a bit of space available, so, have you considered an around the wall layout? You could build it U-shaped or E-shaped, with reversing loops on the ends of the two longer E legs, and with your yard and engine terminal on the middle E leg. If you choose U-shape, your yard and engine terminal would go at the end of one leg with a nice reversing loop at the end of the other leg.
Just something to consider.
Chuck
